Filtration arrangement utilizing pleated construction and method

ABSTRACT

Filter arrangements include a barrier media, usually pleated, treated with a deposit of fine fibers. The media is particularly advantageous at high temperature (greater than 140° F.) systems. Such systems may include engine systems and fluid compressor systems. Filter arrangements may take the form of tubular, radially sealing elements; tubular, axial sealing elements; forward flow air cleaners; reverse flow air cleaners; and panel filters.

RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.09/871,582, filed May 31, 2001, now U.S. Pat. No. 6,800,117 issued Oct.5, 2004, which claims priority under 35 U.S.C. §119(e) to U.S.provisional application serial No. 60/230,138, filed on Sep. 5, 2000,which applications are incorporated by reference herein.

FIELD OF THE INVENTION

The present invention relates to a filter arrangement and filtrationmethod. More specifically, it concerns an arrangement for filteringparticulate material from a gas flow stream, for example, an air stream.The invention also concerns a method for achieving the desirable removalof particulate material from such a gas flow stream.

The present invention is an on-going development of Donaldson CompanyInc., of Minneapolis, Minn., the assignee of the present invention. Thedisclosure concerns continuing technology development related, in part,to the subjects characterized in U.S. Pat. Nos. B2 4,720,292; Des416,308; U.S. Pat. Nos. 5,613,992; 4,020,783; and 5,112,372. Each of thepatents identified in the previous sentence is also owned by Donaldson,Inc., of Minneapolis, Minn.; and, the complete disclosure of each isincorporated herein by reference.

The invention also relates to polymer material and fiber that can bemanufactured with improved environmental stability to heat, humidity,reactive materials and mechanical stress. Such materials can be used inthe formation of fine fibers such as microfibers and nanofiber materialswith improved stability and strength. As the size of fiber is reducedthe survivability of the materials is increasingly more of a problem.Such fine fibers are useful in a variety of applications. In oneapplication, filter structures can be prepared using this fine fibertechnology. The techniques described concern structures having one ormore layers of fine fibers in the filter media. The structure,composition and fiber size are selected for a combination of propertiesand survivability.

BACKGROUND OF THE INVENTION

Gas streams often carry particulate material therein. In many instances,removal of some or all of the particulate material from a gas flowstream is essential. For example, air intake streams to engines formotorized vehicles or power generation equipment, gas streams directedto gas turbines, and air streams to various combustion furnaces, ofteninclude particulate material. The particulate material can causesubstantial damage to operating equipment. The particulate is preferablyremoved from the gas flow upstream of the engine, turbine, furnace orother equipment.

In other instances, production gases or off gases may containparticulate material, for example, those generated by processes thatincluded milling, chemical processing, sintering, painting, etc. Beforesuch gases can be, or should be, directed through various downstreamequipment and/or to the atmosphere, a substantial removal of particulatematerial from those streams is important.

The invention relates to filter elements in structures and to improvedfilter technology. The invention also relates to polymeric compositionswith improved properties that can be used in a variety of relatedapplications including the formation of fibers, microfibers, nanofibers,fiber webs, fibrous mats, permeable structures such as membranes,coatings or films. The polymeric materials of the invention arecompositions that have physical properties that permit the polymericmaterial, in a variety of physical shapes or forms, to have resistanceto the degradative effects of humidity, heat, air flow, chemicals andmechanical stress or impact in filtration structures and methods.

In making non-woven fine fiber filter media, a variety of materials havebeen used including fiberglass, metal, ceramics and a wide range ofpolymeric compositions. A variety of techniques have been used for themanufacture of small diameter micro- and nanofibers. One method involvespassing the material through a fine capillary or opening either as amelted material or in a solution that is subsequently evaporated. Fiberscan also be formed by using “spinnerets” typical for the manufacture ofsynthetic fiber such as nylon. Electrostatic spinning is also known.Such techniques involve the use of a hypodermic needle, nozzle,capillary or movable emitter. These structures provide liquid solutionsof the polymer that are then attracted to a collection zone by a highvoltage electrostatic field. As the materials are pulled from theemitter and accelerate through the electrostatic zone, the fiber becomesvery thin and can be formed in a fiber structure by solvent evaporation.

As more demanding applications are envisioned for filtration media,significantly improved materials are required to withstand the rigors ofhigh temperature 100° F. to 250° F. and up to 300° F., high humidity 10%to 90% up to 100% RH, high flow rates of both gas and liquid, andfiltering micron and submicron particulates (ranging from about 0.01 toover 10 microns) and removing both abrasive and non-abrasive andreactive and non-reactive particulate from the fluid stream.

Accordingly, a substantial need exists for polymeric materials, micro-and nanofiber materials and filter structures that provide improvedproperties for filtering streams with higher temperatures, higherhumidities, high flow rates and said micron and submicron particulatematerials.

SUMMARY OF THE INVENTION

Herein, general techniques for the design and application of air cleanerarrangements are provided. The techniques include preferred filterelement design, as well as the preferred methods of application andfiltering.

In general, the preferred applications concern utilization, within anair filter, of barrier media, typically pleated media, and fine fibers,to advantage.

The filter media includes at least a micro- or nanofiber web layer incombination with a substrate material in a mechanically stable filterstructure. These layers together provide excellent filtering, highparticle capture, efficiency at minimum flow restriction when a fluidsuch as a gas or liquid passes through the filter media. The substratecan be positioned in the fluid stream upstream, downstream or in aninternal layer. A variety of industries have directed substantialattention in recent years to the use of filtration media for filtration,i.e. the removal of unwanted particles from a fluid such as gas or, incertain instances, liquid. The common filtration process removesparticulate from fluids including an air stream or other gaseous streamor from a liquid stream such as a hydraulic fluid, lubricant oil, fuel,water stream or other fluids. Such filtration processes require themechanical strength, chemical and physical stability of the microfiberand the substrate materials. The filter media can be exposed to a broadrange of temperature conditions, humidity, mechanical vibration andshock and both reactive and non-reactive, abrasive or non-abrasiveparticulates entrained in the fluid flow. Further, the filtration mediaoften require the self-cleaning ability of exposing the filter media toa reverse pressure pulse (a short reversal of fluid flow to removesurface coating of particulate) or other cleaning mechanism that canremove entrained particulate from the surface of the filter media. Suchreverse cleaning can result in substantially improved (i.e.) reducedpressure drop after the pulse cleaning. Particle capture efficiencytypically is not improved after pulse cleaning, however pulse cleaningwill reduce pressure drop, saving energy for filtration operation. Suchfilters can often be removed for service and cleaned in aqueous ornon-aqueous cleaning compositions. Such media are often manufactured byspinning fine fiber and then forming a layer, a web or an interlockingweb of microfiber on a porous substrate. In the spinning process thefiber can form physical bonds between fibers to interlock or integratethe layer and to secure the fiber mat into a layer. Such a material canthen be bonded to a substrate, and fabricated into the desired filterformat such as cartridges, flat disks, canisters, panels, bags andpouches. Within such structures, the media can be substantially pleated,rolled or otherwise positioned on support structures. The filterarrangements described herein can be utilized in a wide variety ofapplications including: equipment enclosures, vehicle cabin ventilation,cabin air filters, on-road and off-road engines; and, industrialequipment, such as compressors and other related applications.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a typical electrostatic emitter driven apparatus forproduction of the fine fibers of the invention.

FIG. 2 shows the apparatus used to introduce fine fiber onto filtersubstrate into the fine fiber forming technology shown in FIG. 1.

FIG. 3 is a depiction of the typical internal structure of a supportmaterial and a separate depiction of the fine fiber material of theinvention compared to small, i.e. 2 and 5 micron particulate materials.

FIGS. 4 through 11 are analytical ESCA spectra relating to Example 13.

FIG. 12 shows the stability of the 0.23 and 0.45 microfiber material ofthe invention from Example 5.

FIGS. 13 through 16 show the improved temperature and humidity stabilityof the materials of Examples 5 and 6 when compared to unmodified nyloncopolymer solvent soluble polyamide.

FIGS. 17 through 19 a demonstrate that the blend of two copolymers, anylon homopolymer and a nylon copolymer, once heat treated and combinedwith additives form a single component material that does not displaydistinguishable characteristics of two separate polymer materials, butappears to be a crosslinked or otherwise chemically joined single phase.

FIG. 20 is a schematic view of a system having an engine with an airintake system and an air cleaner therein.

FIG. 21 is a schematic, cross-sectional view of a primary filter elementand a safety filter element mounted therein, both of which are mountedon an air flow tube for use with an engine system such as that depictedin FIG. 20.

FIG. 22 is a side elevational, fragmented view of the primary filterelement depicted in FIG. 21.

FIG. 23 is an enlarged, schematic, fragmented, cross-sectional view ofthe end cap and sealing portion of the primary filter element depictedin FIGS. 21 and 22.

FIG. 24 is a side elevational, fragmented view of the safety elementdepicted in FIG. 21.

FIG. 25 is a side elevational view of another air cleaner that can beutilized with the engine system depicted in FIG. 20.

FIG. 26 is a schematic, exploded, side elevational view of the aircleaner, including the housing and the primary filter element depictedin FIG. 25.

FIG. 27 is an enlarged, cross-sectional view of the primary filterelement operably installed in the air cleaner housing taken along theline 8—8 of FIG. 25.

FIG. 28 is an enlarged, cross-sectional view of another portion of theprimary filter element operably installed in the air cleaner housingtaken along the line 9—9 of FIG. 25.

FIG. 29 is a side elevational, partially fragmented and partiallycross-sectional view of another air cleaner that may be utilized withthe engine system depicted in FIG. 20.

FIG. 30 is a fragmented, side elevational, partially cross-sectionalview of another air cleaner that may be utilized with the engine systemdepicted in FIG. 20.

FIG. 31 is an end elevational, partially fragmented view of the aircleaner depicted in FIG. 30.

FIG. 32 is a side elevational view of a panel filter element that may beutilized with the engine system depicted in FIG. 20.

FIG. 33 is a top plan view of the panel filter depicted in FIG. 32.

FIG. 34 is a schematic view of a system having a fluid compressor withan air intake system and a primary filter element therein.

FIG. 35 is a plan view of an air filter arrangement, with a portionbroken away.

FIG. 36 is a perspective view of a filter assembly (V-pack) utilized inthe air filter arrangement of FIG. 37.

FIG. 37 is a cross-sectional view of the filter assembly taken along theline 20—20 in FIG. 36.

DETAILED DESCRIPTION OF THE INVENTION A. Microfiber or Fine FiberPolymeric Materials

The invention provides an improved polymeric material. This polymer hasimproved physical and chemical stability. The polymer fine fiber, with adiameter of 200 nanometers to 10 microns, (microfiber and nanofiber) canbe fashioned into useful product formats (e.g., when formed onto asubstrate). Nanofiber is a fiber with diameter less than 200 nanometeror 0.2 micron. Microfiber is a fiber with diameter larger than 0.2micron, but not larger than 10 microns. This fine fiber can be made inthe form of an improved multi-layer microfiltration media structure. Thefine fiber layers of the invention comprise a random distribution offine fibers which can be bonded to form an interlocking net.

Filtration performance is obtained largely as a result of the fine fiberbarrier to the passage of particulate. Structural properties ofstiffness, strength, pleatability are provided by the substrate to whichthe fine fiber adhered. The fine fiber interlocking networks have asimportant characteristics, fine fibers in the form of microfibers ornanofibers and relatively small openings, orifices or spaces between thefibers. Such spaces typically range, between fibers, of about 0.01 toabout 25 microns or often about 0.1 to about 10 microns.

The filter products comprise a fine fiber layer formed on a substrate.Fibers from synthetic, natural sources (e.g., polyester and celluloselayers) are thin, appropriate substrate choices. The fine fiber addsless than a micron in thickness to the overall fine fiber plus substratefilter media. In service, the filters can stop incident particulate frompassing through the fine fiber layer and can attain substantial surfaceloadings of trapped particles. The particles comprising dust or otherincident particulates rapidly form a dust cake on the fine fiber surfaceand maintains high initial and overall efficiency of particulateremoval. Even with relatively fine contaminants having a particle sizeof about 0.01 to about 1 micron, the filter media comprising the finefiber has a very high dust capacity.

The polymer materials as disclosed herein have substantially improvedresistance to the undesirable effects of heat, humidity, high flowrates, reverse pulse cleaning, operational abrasion, submicronparticulates, cleaning of filters in use and other demanding conditions.The improved microfiber and nanofiber performance is a result of theimproved character of the polymeric materials forming the microfiber ornanofiber. Further, the filter media of the invention using the improvedpolymeric materials of the invention provides a number of advantageousfeatures including higher efficiency, lower flow restriction, highdurability (stress related or environmentally related) in the presenceof abrasive particulates and a smooth outer surface free of loose fibersor fibrils. The overall structure of the filter materials provides anoverall thinner media allowing improved media area per unit volume,reduced velocity through the media, improved media efficiency andreduced flow restrictions.

The fine fiber can be made of a polymer material or a polymer plusadditive. One preferred mode of the invention is a polymer blendcomprising a first polymer and a second, but different polymer(differing in polymer type, molecular weight or physical property) thatis conditioned or treated at elevated temperature. The polymer blend canbe reacted and formed into a single chemical specie or can be physicallycombined into a blended composition by an annealing process. Annealingimplies a physical change, like crystallinity, stress relaxation ororientation. Preferred materials are chemically reacted into a singlepolymeric specie such that a Differential Scanning Calorimeter analysisreveals a single polymeric material. Such a material, when combined witha preferred additive material, can form a surface coating of theadditive on the microfiber that provides oleophobicity, hydrophobicityor other associated improved stability when contacted with hightemperature, high humidity and difficult operating conditions. The finefiber of the class of materials can have a diameter of about 0.01 to 5microns. Such microfibers can have a smooth surface comprising adiscrete layer of the additive material or an outer coating of theadditive material that is partly solubilized or alloyed in the polymersurface, or both. Preferred materials for use in the blended polymericsystems include nylon 6; nylon 66; nylon 6-10; nylon (6-66-610)copolymers and other linear generally aliphatic nylon compositions. Apreferred nylon copolymer resin (SVP-651) was analyzed for molecularweight by the end group titration. (J. E. Walz and G. B. Taylor,determination of the molecular weight of nylon, Anal. Chem. Vol. 19,Number 7, pp 448-450 (1947). A number average molecular weight (M_(n))was between 21,500 and 24,800. The composition was estimated by thephase diagram of melt temperature of three component nylon, nylon 6about 45%, nylon 66 about 20% and nylon 610 about 25%. (Page 286, NylonPlastics Handbook, Melvin Kohan ed. Hanser Publisher, New York (1995)).

Reported physical properties of SVP 651 resin are:

Property ASTM Method Units Typical Value Specific Gravity D-792 —  1.08Water Absorption D-570 %  2.5 (24 hr immersion) Hardness D-240 Shore D 65 Melting Point DSC ° C. (° F.) 154 (309) Tensile Strength D-638 MPa(kpsi)  50 (7.3) @ Yield Elongation at Break D-638 % 350 FlexuralModulus D-790 MPa (kpsi) 180 (26) Volume Resistivity D-257 ohm-cm  10¹²

A polyvinylalcohol having a hydrolysis degree of from 87 to 99.9+% canbe used in such polymer systems. These are preferably cross linked byphysical or chemical agents. These PVOH polymers are most preferablycrosslinked and combined with substantial quantities of the oleophobicand hydrophobic additive materials.

Another preferred mode of the invention involves a single polymericmaterial combined with an additive composition to improve fiber lifetimeor operational properties. The preferred polymers useful in this aspectof the invention include both condensation polymers and additivepolymers such as nylon polymers, polyvinylidene chloride polymers,polyvinylidene fluoride polymers, polyvinylalcohol polymers and, inparticular, those listed materials when combined with stronglyoleophobic and hydrophobic additives that can result in a microfiber ornanofiber with the additive materials formed in a coating on the finefiber surface. Again, blends of similar polymers such as a blend ofsimilar nylons, similar polyvinylchloride polymers, blends ofpolyvinylidene chloride polymers are useful in this invention. Further,polymeric blends or alloys of differing polymers are also contemplatedby the invention. In this regard, compatible mixtures of polymers areuseful in forming the microfiber materials of the invention. Additivecomposition such a fluoro-surfactant, a nonionic surfactant, lowmolecular weight resins (e.g.) tertiary butylphenol resin having amolecular weight of less than about 3000 can be used. The resin ischaracterized by oligomeric bonding between phenol nuclei in the absenceof methylene bridging groups. The positions of the hydroxyl and thetertiary butyl group can be randomly positioned around the rings.Bonding between phenolic nuclei always occurs next to hydroxyl group,not randomly. Similarly, the polymeric material can be combined with analcohol soluble non-linear polymerized resin formed from bis-phenol A.Such material is similar to the tertiary butylphenol resin describedabove in that it is formed using oligomeric bonds that directly connectaromatic ring to aromatic ring in the absence of any bridging groupssuch as alkylene or methylene groups.

A particularly preferred material of the invention comprises amicrofiber material having a dimension of about 0.001 to 10 microns. Apreferred fiber size range between 0.05 to 0.5 micron. Depending on enduse and pulse cleaner or cleaning options, the fiber may be selectedfrom 0.01 to 2 microns fiber, from 0.005 to 5 microns fiber or from 0.1to 10 microns fiber. Such fibers with the preferred size provideexcellent filter activity, ease of back pulse cleaning and otheraspects. The highly preferred polymer systems of the invention haveadhering characteristic such that when contacted with a cellulosicsubstrate adheres to the substrate with sufficient strength such that itis securely bonded to the substrate and can resist the delaminatingeffects of a reverse pulse cleaning technique and other mechanicalstresses. In such a mode, the polymer material must stay attached to thesubstrate while undergoing a pulse clean input that is substantiallyequal to the typical filtration conditions except in a reverse directionacross the filter structure. Such adhesion can arise from solventeffects of fiber formation as the fiber is contacted with the substrateor the post treatment of the fiber on the substrate with heat orpressure. However, polymer characteristics appear to play an importantrole in determining adhesion, such as specific chemical interactionslike hydrogen bonding, contact between polymer and substrate occurringabove or below Tg, and the polymer formulation including additives.Polymers plasticized with solvent or steam at the time of adhesion canhave increased adhesion.

An important aspect of the invention is the utility of such microfiberor nanofiber materials formed into a filter structure. In such astructure, the fine fiber materials of the invention are formed on andadhered to a filter substrate. Natural fiber and synthetic fibersubstrates, like spun bonded fabrics, non-woven fabrics of syntheticfiber and non-wovens made from the blends of cellulosics, synthetic andglass fibers, non-woven and woven glass fabrics, plastic screen likematerials both extruded and hole punched, UF and MF membranes of organicpolymers can be used. Sheet-like substrate or cellulosic non-woven webcan then be formed into a filter structure that is placed in a fluidstream including an air stream or liquid stream for the purpose ofremoving suspended or entrained particulate from that stream. The shapeand structure of the filter material is up to the design engineer. Oneimportant parameter of the filter elements after formation is itsresistance to the effects of heat, humidity or both. One aspect of thefilter media of the invention is a test of the ability of the filtermedia to survive immersion in warm water for a significant period oftime. The immersion test can provide valuable information regarding theability of the fine fiber to survive hot humid conditions and to survivethe cleaning of the filter element in aqueous solutions that can containsubstantial proportions of strong cleaning surfactants and strongalkalinity materials. Preferably, the fine fiber materials of theinvention can survive immersion in hot water while retaining at least50% of the fine fiber formed on the surface of the substrate as anactive filter component. Retention of at least 50% of the fine fiber canmaintain substantial fiber efficiency without loss of filtrationcapacity or increased back pressure. Most preferably retaining at least75%.

The fine fibers that comprise the micro- or nanofiber containing layerof the invention can be fiber and can have a diameter of about 0.001 to10 microns, preferably 0.05 to 0.5 micron. The thickness of the typicalfine fiber filtration layer ranges from about 1 to 100 times the fiberdiameter with a basis weight ranging from about 0.01 to 240micrograms-cm⁻².

Fluid streams such as air and gas streams often carry particulatematerial therein. The removal of some or all of the particulate materialfrom the fluid stream is needed. For example, air intake streams to thecabins of motorized vehicles, air in computer disk drives, HVAC air,clean room ventilation and applications using filter bags, barrierfabrics, woven materials, air to engines for motorized vehicles, or topower generation equipment; gas streams directed to gas turbines; and,air streams to various combustion furnaces, often include particulatematerial therein. In the case of cabin air filters it is desirable toremove the particulate matter for comfort of the passengers and/or foraesthetics. With respect to air and gas intake streams to engines, gasturbines and combustion furnaces, removal of the particulate material isneeded because particulate can cause substantial damage to the internalworkings to the various mechanisms involved. In other instances,production gases or off gases from industrial processes or engines maycontain particulate material therein. Before such gases can be, orshould be, discharged through various downstream equipment to theatmosphere, it may be desirable to obtain a substantial removal ofparticulate material from those streams.

A general understanding of some of the basic principles and problems ofair filter design can be understood by consideration of the followingtypes of filter media: surface loading media; and, depth media. Each ofthese types of media has been well studied, and each has been widelyutilized. Certain principles relating to them are described, forexample, in U.S. Pat. Nos. 5,082,476; 5,238,474; and 5,364,456. Thecomplete disclosures of these three patents are incorporated herein byreference.

The “lifetime” of a filter is typically defined according to a selectedlimiting pressure drop across the filter. The pressure buildup acrossthe filter defines the lifetime at a defined level for that applicationor design. Since this buildup of pressure is a result of load, forsystems of equal efficiency a longer life is typically directlyassociated with higher capacity. Efficiency is the propensity of themedia to trap, rather than pass, particulates. Typically the moreefficient a filter media is at removing particulates from a gas flowstream, in general, the more rapidly the filter media will approach the“lifetime” pressure differential (assuming other variables to be heldconstant). In this application the term “unchanged for filtrationpurposes” refers to maintaining sufficient efficiency to removeparticulate from the fluid stream as is necessary for the selectedapplication.

Polymeric materials have been fabricated in non-woven and woven fabrics,fibers and microfibers. The polymeric material provides the physicalproperties required for product stability. These materials should notchange significantly in dimension, suffer reduced molecular weight,become less flexible or subject to stress cracking or physicallydeteriorate in the presence of sunlight, humidity, high temperatures orother negative environmental effects. The invention relates to animproved polymeric material that can maintain physical properties in theface of incident electromagnetic radiation such as environmental light,heat, humidity and other physical challenges.

Polymer materials that can be used in the polymeric compositions of theinvention include both addition polymer and condensation polymermaterials such as polyolefin, polyacetal, polyamide, polyester,cellulose ether and ester, polyalkylene sulfide, polyarylene oxide,polysulfone, modified polysulfone polymers and mixtures thereof.Preferred materials that fall within these generic classes includepolyethylene, polypropylene, poly(vinylchloride), polymethylmethacrylate(and other acrylic resins), polystyrene, and copolymers thereof(including ABA type block copolymers), poly(vinylidene fluoride),poly(vinylidene chloride), polyvinylalcohol in various degrees ofhydrolysis (87% to 99.5%) in crosslinked and non-crosslinked forms.Preferred addition polymers tend to be glassy (a Tg greater than roomtemperature). This is the case for polyvinylchloride andpolymethylmethacrylate, polystyrene polymer compositions or alloys orlow in crystallinity for polyvinylidene fluoride and polyvinylalcoholmaterials. One class of polyamide condensation polymers are nylonmaterials. The term “nylon” is a generic name for all long chainsynthetic polyamides. Typically, nylon nomenclature includes a series ofnumbers such as in nylon-6,6 which indicates that the starting materialsare a C₆ diamine and a C₆ diacid (the first digit indicating a C₆diamine and the second digit indicating a C₆ dicarboxylic acidcompound). Another nylon can be made by the polycondensation of epsilon(C₆) caprolactam (or other C₆₋₁₂ lactams) in the presence of a smallamount of water. This reaction forms a nylon-6 (made from a cycliclactam—also known as episilon-aminocaproic acid) that is a linearpolyamide. Further, nylon copolymers are also contemplated. Copolymerscan be made by combining various diamine compounds, various diacidcompounds and various cyclic lactam structures in a reaction mixture andthen forming the nylon with randomly positioned monomeric materials in apolyamide structure. For example, a nylon 6,6-6,10 material is a nylonmanufactured from hexamethylene diamine and a C₆ and a C₁₀ blend ofdiacids. A nylon 6-6,6-6,10 is a nylon manufactured by copolymerizationof epsilonaminocaproic acid, hexamethylene diamine and a blend of a C₆and a C₁₀ diacid material.

Block copolymers are also useful in the process of this invention. Withsuch copolymers the choice of solvent swelling agent is important. Theselected solvent is such that both blocks were soluble in the solvent.One example is a ABA (styrene-EP-styrene) or AB (styrene-EP) polymer inmethylene chloride solvent. If one component is not soluble in thesolvent, it will form a gel. Examples of such block copolymers areKraton® type of styrene-b-butadiene and styrene-b-hydrogenatedbutadiene(ethylene propylene), Pebax® type of e-caprolactam-b-ethyleneoxide, Sympatex® polyester-b-ethylene oxide and polyurethanes ofethylene oxide and isocyanates.

Addition polymers like polyvinylidene fluoride, syndiotacticpolystyrene, copolymer of vinylidene fluoride and hexafluoropropylene,polyvinyl alcohol, polyvinyl acetate, amorphous addition polymers, suchas poly(acrylonitrile) and its copolymers with acrylic acid andmethacrylates, polystyrene, poly(vinyl chloride) and its variouscopolymers, poly(methyl methacrylate) and its various copolymers, can besolution spun with relative ease because they are soluble at lowpressures and temperatures. However, highly crystalline polymer likepolyethylene and polypropylene require high temperature, high pressuresolvent if they are to be solution spun. Therefore, solution spinning ofthe polyethylene and polypropylene is very difficult. Electrostaticsolution spinning is one method of making nanofibers and microfiber.

We have also found a substantial advantage to forming polymericcompositions comprising two or more polymeric materials in polymeradmixture, alloy format or in a crosslinked chemically bonded structure.We believe such polymer compositions improve physical properties bychanging polymer attributes such as improving polymer chain flexibilityor chain mobility, increasing overall molecular weight and providingreinforcement through the formation of networks of polymeric materials.

In one embodiment of this concept, two related polymer materials can beblended for beneficial properties. For example, a high molecular weightpolyvinylchloride can be blended with a low molecular weightpolyvinylchloride. Similarly, a high molecular weight nylon material canbe blended with a low molecular weight nylon material. Further,differing species of a general polymeric genus can be blended. Forexample, a high molecular weight styrene material can be blended with alow molecular weight, high impact polystyrene. A Nylon-6 material can beblended with a nylon copolymer such as a Nylon-6; 6,6; 6,10 copolymer.Further, a polyvinylalcohol having a low degree of hydrolysis such as a87% hydrolyzed polyvinylalcohol can be blended with a fully orsuperhydrolyzed polyvinylalcohol having a degree of hydrolysis between98 and 99.9% and higher. All of these materials in admixture can becrosslinked using appropriate crosslinking mechanisms. Nylons can becrosslinked using crosslinking agents that are reactive with thenitrogen atom in the amide linkage. Polyvinylalcohol materials can becrosslinked using hydroxyl reactive materials such as monoaldehydes,such as formaldehyde, ureas, melamine-formaldehyde resin and itsanalogues, boric acids and other inorganic compounds. dialdehydes,diacids, urethanes, epoxies and other known crosslinking agents.Crosslinking technology is a well known and understood phenomenon inwhich a crosslinking reagent reacts and forms covalent bonds betweenpolymer chains to substantially improve molecular weight, chemicalresistance, overall strength and resistance to mechanical degradation.

We have found that additive materials can significantly improve theproperties of the polymer materials in the form of a fine fiber. Theresistance to the effects of heat, humidity, impact, mechanical stressand other negative environmental effect can be substantially improved bythe presence of additive materials. We have found that while processingthe microfiber materials of the invention, that the additive materialscan improve the oleophobic character, the hydrophobic character and canappear to aid in improving the chemical stability of the materials. Webelieve that the fine fibers of the invention in the form of amicrofiber are improved by the presence of these oleophobic andhydrophobic additives as these additives form a protective layercoating, ablative surface or penetrate the surface to some depth toimprove the nature of the polymeric material. We believe the importantcharacteristics of these materials are the presence of a stronglyhydrophobic group that can preferably also have oleophobic character.Strongly hydrophobic groups include fluorocarbon groups, hydrophobichydrocarbon surfactants or blocks and substantially hydrocarbonoligomeric compositions. These materials are manufactured incompositions that have a portion of the molecule that tends to becompatible with the polymer material affording typically a physical bondor association with the polymer while the strongly hydrophobic oroleophobic group, as a result of the association of the additive withthe polymer, forms a protective surface layer that resides on thesurface or becomes alloyed with or mixed with the polymer surfacelayers. The additive can be used at an amount of 1% to 25% by weighttotal on fiber. For 0.2-micron fiber with 10% additive level, thesurface thickness is calculated to be around 50 Å, if the additive hasmigrated toward the surface. Migration is believed to occur due to theincompatible nature of the oleophobic or hydrophobic groups in the bulkmaterial. A 50 Å thickness appears to be reasonable thickness forprotective coating. For 0.05-micron diameter fiber, 50 Å thicknesscorresponds to 20% mass. For 2 microns thickness fiber, 50 Å thicknesscorresponds to 2% mass. Preferably the additive materials are used at anamount of about 2 to 25 wt. %. Useful surface thickness can range from10 Å to 150 Å.

Oligomeric additives that can be used in combination with the polymermaterials of the invention include oligomers having a molecular weightof about 500 to about 5000, preferably about 500 to about 3000 includingfluoro-chemicals, nonionic surfactants and low molecular weight resinsor oligomers. Fluoro-organic wetting agents useful in this invention areorganic molecules represented by the formulaR_(f)-Gwherein R_(f) is a fluoroaliphatic radical and G is a group whichcontains at least one hydrophilic group such as cationic, anionic,nonionic, or amphoteric groups. Nonionic materials are preferred. R_(f)is a fluorinated, monovalent, aliphatic organic radical containing atleast two carbon atoms. Preferably, it is a saturated perfluoroaliphaticmonovalent organic radical. However, hydrogen or chlorine atoms can bepresent as substituents on the skeletal chain. While radicals containinga large number of carbon atoms may function adequately, compoundscontaining not more than about 20 carbon atoms are preferred since largeradicals usually represent a less efficient utilization of fluorine thanis possible with shorter skeletal chains. Preferably, R_(f) containsabout 2 to 8 carbon atoms.

The cationic groups that are usable in the fluoro-organic agentsemployed in this invention may include an amine or a quaternary ammoniumcationic group which can be oxygen-free (e.g., —NH₂) oroxygen-containing (e.g., amine oxides). Such amine and quaternaryammonium cationic hydrophilic groups can have formulas such as —NH₂,—(NH₃)X, —(NH(R²)₂)X, —(NH(R²)₃)X, or —N(R₂)₂→O, where x is an anioniccounterion such as halide, hydroxide, sulfate, bisulfate, orcarboxylate, R² is H or C₁₋₁₈ alkyl group, and each R² can be the sameas or different from other R² groups. Preferably, R² is H or a C₁₋₁₆alkyl group and X is halide, hydroxide, or bisulfate.

The anionic groups which are usable in the fluoro-organic wetting agentsemployed in this invention include groups which by ionization can becomeradicals of anions. The anionic groups may have formulas such as —COOM,—SO₃M, —OSO₃M, —PO₃HM, —OPO₃M₂, or —OPO₃HM, where M is H, a metal ion,(NR¹ ₄)⁺, or (SR¹ ₄)⁺, where each R¹ is independently H or substitutedor unsubstituted C₁-C₆ alkyl. Preferably M is Na⁺ or K⁺. The preferredanionic groups of the fluoro-organo wetting agents used in thisinvention have the formula —COOM or —SO₃M. Included within the group ofanionic fluoro-organic wetting agents are anionic polymeric materialstypically manufactured from ethylenically unsaturated carboxylic mono-and diacid monomers having pendent fluorocarbon groups appended thereto.Such materials include surfactants obtained from 3M Corporation known asFC-430 and FC-431.

The amphoteric groups which are usable in the fluoro-organic wettingagent employed in this invention include groups which contain at leastone cationic group as defined above and at least one anionic group asdefined above.

The nonionic groups which are usable in the fluoro-organic wettingagents employed in this invention include groups which are hydrophilicbut which under pH conditions of normal agronomic use are not ionized.The nonionic groups may have formulas such as —O(CH₂CH₂)xOH where x isgreater than 1, —SO₂NH₂, —SO₂NHCH₂CH₂OH, —SO₂N(CH₂CH₂H)₂, —CONH₂,—CONHCH₂CH₂OH, or —CON(CH₂CH₂OH)₂. Examples of such materials includematerials of the following structure:F(CF₂CF₂)_(n)—CH₂CH₂O—(CH₂CH₂O)_(m)—Hwherein n is 2 to 8 and m is 0 to 20.

Other fluoro-organic wetting agents include those cationicfluorochemicals described, for example in U.S. Pat. Nos. 2,764,602;2,764,603; 3,147,064 and 4,069,158. Such amphoteric fluoro-organicwetting agents include those amphoteric fluorochemicals described, forexample, in U.S. Pat. Nos. 2,764,602; 4,042,522; 4,069,158; 4,069,244;4,090,967; 4,161,590 and 4,161,602. Such anionic fluoro-organic wettingagents include those anionic fluorochemicals described, for example, inU.S. Pat. Nos. 2,803,656; 3,255,131; 3,450,755 and 4,090,967.

Examples of such materials are duPont Zonyl FSN and duPont Zonyl FSOnonionic surfactants. Another aspect of additives that can be used inthe polymers of the invention include low molecular weight fluorocarbonacrylate materials such as 3M's Scotchgard material having the generalstructure:CF₃(CX₂)_(n)-acrylatewherein X is, independently, —F or —CF₃ and n is 1 to 7.

Further, nonionic hydrocarbon surfactants including lower alcoholethoxylates, fatty acid ethoxylates, nonylphenol ethoxylates, etc. canalso be used as additive materials for the invention. Examples of thesematerials include Triton X-100 and Triton N-101.

A useful material for use as an additive material in the compositions ofthe invention are tertiary butylphenol oligomers. Such materials tend tobe relatively low molecular weight aromatic phenolic resins. Such resinsare phenolic polymers prepared by enzymatic oxidative coupling. Theabsence of methylene bridges result in unique chemical and physicalstability. These phenolic resins can be crosslinked with various aminesand epoxies and are compatible with a variety of polymer materials.These materials are generally exemplified by the following structuralformulas which are characterized by phenolic materials in a repeatingmotif in the absence of methylene bridge groups having phenolic andaromatic groups.

wherein n is 2 to 20. Examples of these phenolic materials includeEnzo-BPA, Enzo-BPA/phenol, Enzo-TBP, Enzo-COP and other relatedphenolics were obtained from Enzymol International Inc., Columbus, Ohio.

It should be understood that an extremely wide variety of fibrous filtermedia exist for different applications. The durable nanofibers andmicrofibers described in this invention can be added to any of themedia. The fibers described in this invention can also be used tosubstitute for fiber components of these existing media giving thesignificant advantage of improved performance (improved efficiencyand/or reduced pressure drop) due to their small diameter, whileexhibiting greater durability.

Polymer nanofibers and microfibers are known, however their use has beenvery limited due to their fragility to mechanical stresses, and theirsusceptibility to chemical degradation due to their very high surfacearea to volume ratio. The fibers described in this invention addressthese limitations and will therefore be usable in a very wide variety offiltration, textile, membrane and other diverse applications.

DETAILED DESCRIPTION OF CERTAIN DRAWINGS

The microfiber or nanofiber of the unit can be formed by theelectrostatic spinning process. A suitable apparatus for forming thefiber is illustrated in FIG. 1. This apparatus includes a reservoir 80in which the fine fiber forming polymer solution is contained, a pump 81and a rotary type emitting device or emitter 40 to which the polymericsolution is pumped. The emitter 40 generally consists of a rotatingunion 41, a rotating portion 42 including a plurality of offset holes 44and a shaft 43 connecting the forward facing portion and the rotatingunion. The rotating union 41 provides for introduction of the polymersolution to the forward facing portion 42 through the hollow shaft 43.The holes 44 are spaced around the periphery of the forward facingportion 42. Alternatively, the rotating portion 42 can be immersed intoa reservoir of polymer fed by reservoir 80 and pump 81. The rotatingportion 42 then obtains polymer solution from the reservoir and as itrotates in the electrostatic field, a droplet of the solution isaccelerated by the electrostatic field toward the collecting media 70 asdiscussed below.

Facing the emitter 40, but spaced apart therefrom, is a substantiallyplanar grid 60 upon which the collecting media 70 (i.e. substrate orcombined substrate is positioned. Air can be drawn through the grid. Thecollecting media 70 is passed around rollers 71 and 72 which arepositioned adjacent opposite ends of grid 60. A high voltageelectrostatic potential is maintained between emitter 40 and grid 60 bymeans of a suitable electrostatic voltage source 61 and connections 62and 63 which connect respectively to the grid 60 and emitter 40.

In use, the polymer solution is pumped to the rotating union 41 orreservoir from reservoir 80. The forward facing portion 42 rotates whileliquid exits from holes 44, or is picked up from a reservoir, and movesfrom the outer edge of the emitter toward collecting media 70 positionedon grid 60. Specifically, the electrostatic potential between grid 60and the emitter 40 imparts a charge to the material which cause liquidto be emitted therefrom as thin fibers which are drawn toward grid 60.In the case of the polymer in solution, solvent is evaporated off thefibers during their flight to the grid 60. The fine fibers bond to thesubstrate fibers first encountered at the grid 60. Electrostatic fieldstrength is selected to ensure that the polymer material as it isaccelerated from the emitter to the collecting media 70, theacceleration is sufficient to render the material into a very thinmicrofiber or nanofiber structure. Increasing or slowing the advancerate of the collecting media can deposit more or less emitted fibers onthe forming media, thereby allowing control of the thickness of eachlayer deposited thereon. The rotating portion 42 can have a variety ofbeneficial positions. The rotating portion 42 can be placed in a planeof rotation such that the plane is perpendicular to the surface of thecollecting media 70 or positioned at any arbitrary angle. The rotatingmedia can be positioned parallel to or slightly offset from parallelorientation.

FIG. 2 is a general schematic diagram of a process and apparatus forforming a layer of fine fiber on a sheet-like substrate or media. InFIG. 2, the sheet-like substrate is unwound at station 20. Thesheet-like substrate 20 a is then directed to a splicing station 21wherein multiple lengths of the substrate can be spliced for continuousoperation. The continuous length of sheet-like substrate is directed toa fine fiber technology station 22 comprising the spinning technology ofFIG. 1 wherein a spinning device forms the fine fiber and lays the finefiber in a filtering layer on the sheet-like substrate. After the finefiber layer is formed on the sheet-like substrate in the formation zone22, the fine fiber layer and substrate are directed to a heat treatmentstation 23 for appropriate processing. The sheet-like substrate and finefiber layer is then tested in an efficiency monitor 24 (see U.S. Pat.No. 5,203,201 which is expressly incorporated by reference herein forprocess and monitoring purposes) and nipped if necessary at a nipstation 25. The sheet-like substrate and fiber layer is then steered tothe appropriate winding station to be wound onto the appropriate spindlefor further processing 26 and 27.

FIG. 3 is a scanning electromicrograph image showing the relationship oftypical dust particles having a diameter of about 2 and about 5 micronswith respect to the sizes of pores in typical cellulose media and in thetypical fine fiber structures. In FIG. 3A, the 2 micron particle 31 andthe 5 micron particle 32 is shown in a cellulosic media 33 with poresizes that are shown to be quite a bit larger than the typical particlediameters. In sharp contrast, in FIG. 3B, the 2 micron particle appearsto be approximately equal to or greater than the typical openingsbetween the fibers in the fiber web 35 while the 5 micron particle 32appears to be larger than any of the openings in the fine fiber web 35.

We have found that filters in storage or transportation to end use canbe exposed to extremes in environmental conditions. Filters in SaudiArabian desert can be exposed to temperature as high as 150° F. orhigher. Filters installed in Indonesia or Gulf Coast of US can beexposed high humidity above 90% RH and high temperature of 100° F. Or,they can be exposed to rain. We have found that filters used under thehood of mobile equipment like cars, trucks, buses, tractors, andconstruction equipment can be exposed to high temperature (180° F. to280° F.), high relative humidity and other chemical environment. Whenoperating normally the filter temperature is generally at ambient. Thistemperature condition is most severe when the equipment or engine isoperating abnormally or is used at or near maximum power and is thenshut down. We have developed test methods to evaluate survivability ofmicrofiber systems under harsh conditions. Soaking the filter mediasamples in hot water (140° F.) for 5 minutes or exposure to highhumidity, high temperature and air flow.

B. General Principles Relating to Air Cleaner Design

Herein, the term “air cleaner” will be used in reference to a systemwhich functions to remove particulate material from an air flow stream.The term “air filter” references a system in which removal is conductedby passage of the air, carrying particulate therein, through filtermedia. The term “filter media” or “media” refers to a material orcollection of material through which the air passes, with a concomitantdeposition of the particles in or on the media. The term “surfaceloading media” or “barrier media” refers to a system in which as the airpasses through the media, the particulate material is primarilydeposited on the surface of the media, forming a filter cake, as opposedto into or through the depth of the media. Herein the term “filterelement” is generally meant to refer to a portion of the air cleanerwhich includes the filter media therein. In general, a filter elementwill be designed as a removable and replaceable, i.e. serviceable,portion of the air cleaner. That is, the filter media will be carried bythe filter element and be separable from the remainder portion of theair cleaner so that periodically the air cleaner can be rejuvenated byremoving a loaded or partially loaded filter element and replacing itwith a new, or cleaned, filter element. Preferably, the air cleaner isdesigned so that the removal and replacement can be conducted by hand.By the term “loaded” or variants thereof in this context, reference ismeant to an air cleaner which has been on-line a sufficient period oftime to contain a significant amount of trapped particles orparticulates thereon, for example, at least a weight gain of 5%. In manyinstances, during normal operation, a filter element will increase inweight, due to particulate loading therein, of two or three times (ormore) its original weight. The fine fiber layers formed on the substratein the filters of the invention should be substantially uniform in bothfiltering performance and fiber location. By substantial uniformity, wemean that the fiber has sufficient coverage of the substrate to have atleast some measurable filtration efficiency throughout the coveredsubstrate. Adequate filtration can occur with wide variation in fiberadd-on. Accordingly, the fine fiber layers can vary in fiber coverage,basis weight, layer thickness or other measurement of fiber add-on andstill remain well within the bounds of the invention. Even a relativelysmall add-on of fine fiber can add efficiency to the overall filterstructure.

Herein, in some instances references will be made to “on-road” and“off-road” elements. In general, a typical difference between on-roadand off-road element design and use concerns the presence of a “safetyelement”. More specifically, in many instances, off-road filter elementsare utilized in association with the safety elements. For forward flowarrangements, the safety element is generally a cylindrical element thatis positioned inside of the “primary” element during use. The term“primary”, in this and similar contexts, is meant to refer to theelement which conducts the majority of particle collection, in normaluse. Typically, it will be the more “upstream” element, if a safetyelement is involved. Herein, when the term “element” is used, referenceis meant to the primary element, if a safety element is involved.Reference to safety elements will generally be specific by the use ofthe term “safety”.

In the filter art, elements are often referenced with respect to whetherthey are constructed for “light duty”, “medium duty” or “heavy duty”application. With respect to on-road, the specification generallyrelates to the minimum expected lifetime for the element, in terms ofmiles of operation of the vehicle involved. Typical light dutyapplications or elements are constructed and arranged to operateeffectively for at least 20,000 miles, typically at least 30,000 miles.Medium duty elements are generally ones constructed and arranged tooperate for an average of at least 40,000 miles, typically at least50,000 miles. Heavy duty elements are elements constructed and arrangedto operate for at least about 90,000 miles, typically 100,000 miles orlonger. Of course, the characterization is on a continuum. An elementdesigned for 80,000 miles, for example, might be classified by some as aheavy duty element.

Off-road elements are also generally characterized as light duty, mediumduty or heavy duty elements. For off-duty specifications, however, thedefinitions are generally with respect to expected hours of use, priorto filter element change. In general, light duty elements, for off-roaduse, are elements constructed and arranged for an expected operationperiod of at least about 90 hours and typically at least 100 hourswithout changeout; medium duty elements are generally constructed andarranged for operation in the field for at least about 225 hours,typically at least 250 hours, without changeout; and, heavy dutyelements are generally elements constructed and arranged to be used inthe field for at least about 450 hours, typically at least 500 hours,without changeout. Again, a continuum is involved.

In general, specifications for the performance of an air cleaner systemare, generated by the preferences of the original equipment manufacturer(OEM) for the engine involved and/or the OEM of the truck or otherequipment involved. While a wide variety of specifications may beinvolved, some of the major ones are the following:

-   -   1. Engine air intake need (rated flow)    -   2. Initial Restriction    -   3. Initial efficiency    -   4. Average or overall operating restriction    -   5. Overall efficiency    -   6. Filter service life

The engine air intake need is a function of the engine size, i.e.,displacement and rpm at maximum, full or “rated” load. In general, it isthe product of displacement and rated rpm, modified by the volumetricefficiency, a factor which reflects turbo efficiency, duct efficiency,etc. In general, it is a measurement of the volume of air, per unittime, required by the engine or other system involved, during ratedoperation or full load. While air intake need will vary depending uponrpm, the air intake requirement is defined at a rated rpm, often at 1800rpm or 2100 rpm for many typical truck engines. Herein this will becharacterized as the “rated air flow” or by similar terms. The filtercan be expose to air flows as low as 1 to 3 cfm (about 1 cfm per HP)from small engine air intake applications with engine power of about 2to 8 HP. Larger engines consume an intake air flow of 50 to 1000 cfm,often 100 to 800 cfm. In general the filter must be rated to permit flowat least at the rated amount or higher without failure. In otherapplications In general, principles characterized herein can be appliedto air cleaner arrangements used with systems specified for operationover a wide range of ratings or demands, including, for example, ones inthe range of about 50 cubic feet/min. (cfm) up to 10,000 cfm. Suchequipment includes, for example: automotive engines, pickup trucks andsport utility vehicle engines, engines for small trucks and deliveryvehicles, buses, over-the-highway trucks, agricultural equipment (forexample tractors), construction equipment, mining equipment, marineengines, a variety of generator engines, and, in some instances, gasturbines and air compressors.

Air cleaner overall efficiency is generally a reflection of the amountof “filterable” solids which pass into the air cleaner during use, andwhich are retained by the air cleaner. It is typically represented asthe percentage of solids passing into the air cleaner which are retainedby the air cleaner in normal use, on a weight basis. It is evaluated andreported for many systems by using SAE standards, which techniques aregenerally characterized in U.S. Pat. No. 5,423,892 at Column 25, line60-Column 26, line 59; Column 27, lines 1-40. A typical standard used isSAE J726, incorporated herein by reference.

With respect to efficiency, engine manufacturer and/or equipmentmanufacturer specifications will vary, in many instances, withefficiency demands (based on either SAE J726 or field testing) foroverall operation often being set at 99.5% or higher, typically at 99.8%or higher. With typical vehicle engines having air flow demands of 500cfm or above, specifications of 99.8% overall average, or higher, arenot uncommon.

Initial efficiency is the measurable efficiency of the filter when it isfirst put on line. As explained in U.S. Pat. No. 5,423,892 at Column 27,lines 1-40, especially with conventional pleated paper (barrier type orsurface-loading) filters, initial efficiency is generally substantiallylower than the overall average efficiency during use. This is becausethe “dust cake” or contaminant build-up on the surface of such a filterduring operation, increases the efficiency of the filter. Initialefficiency is also often specified by the engine manufacturer and/or thevehicle manufacturer. With typical vehicle engines having air flowdemands of 500 cfm or above, specifications of 98% or above (typically98.5% or above) are common.

Restriction is the pressure differential across an air cleaner or aircleaner system during operation. Contributors to the restrictioninclude: the filter media through which the air is directed; duct sizethrough which the air is directed; and, structural features againstwhich or around which the air is directed as it flows through the aircleaner and into the engine. With respect to air cleaners, initialrestriction limits are often part of the specifications and demands ofthe engine manufacturer and/or equipment manufacturer. This initialrestriction would be the pressure differential measured across the aircleaner when the system is put on line with a clean air filter thereinand before significant loading occurs. Typically, the specifications forany given system have a maximum initial restriction requirement.

In general, engine and equipment manufacturers design equipment withspecifications for air cleaner efficiency up to a maximum restriction.As reported in U.S. Pat. No. 5,423,892, at Column 2, lines 19-29; and,column 6, line 47, column 7, line 3, the limiting restriction: fortypical truck engines is a pressure drop of about 20-30 inches of water,often about 25 inches of water; for automotive internal combustionengines is about 20-25 inches of water; for gas turbines, is typicallyabout 5 inches of water; and, for industrial ventilation systems, istypically about 3 inches of water.

In general, some of the principal variables of concern in air cleanerdesign in order to develop systems to meet the types of specificationscharacterized in the previous section, are the following:

-   -   1. filter media type, geometry and efficiency;    -   2. air cleaner shape and structure; and    -   3. filter element size.

For example, conventional cellulose fiber media or similar media isgenerally a “barrier” filter. An example is paper media. In general, theoperation of such media is through surface loading, i.e., when air isdirected through the media, the surface of the media acts as a barrieror sieve, preventing passage of particulate material therethrough. Intime, a dust cake builds on the surface of the media, increasing mediaefficiency. In general, the “tightness” or “porosity” of the fiberconstruction determines the efficiency, especially the initialefficiency, of the system. In time, the filter cake will effect(increase) the efficiency.

In general, such media is often defined or specified by itspermeability. The permeability test for media is generally characterizedin U.S. Pat. No. 5,672,399 at Col. 19, lines 27-39. In general, it isthe media face velocity (air) required to induce a 0.50 inch waterrestriction across a flat sheet of the referenced material, media orcomposite. Permeability, as used herein, is assessed by a Frazier PermTest, according to ASTM D737 incorporated herein by reference, forexample using a Frazier Perm Tester available from Frazier PrecisionInstrument Co., Inc., Gaithersburg, Md., or by some analogous test.

The permeability of cellulose fiber media used in many types of enginefilters for trucks having rated air flows fibers of 500 cfm or moremanufactured by Donaldson Company, is media having a permeability ofless than about 15 fpm, typically around 13 fpm. In general, in theengine filtration market, for such equipment, a variety of barrier media(pleated media) having permeability values of less than about 25 fpm,and typically somewhere within the range of 10-25 fpm, have been widelyutilized by various element manufacturers.

With respect to media geometry, in general, with barrier filters,preferred geometries are typically pleated, cylindrical, patterns. Suchcylindrical patterns are generally preferred because they are relativelystraightforward to manufacture, use conventional filter manufacturingtechniques, and are relatively easy to service. The pleating of surfaceloading media increases the surface area positioned within a givenvolume. Generally, major parameters with respect to such mediapositioning are: pleat depth; pleat density, typically measured as anumber of pleats per inch along the inner diameter of the pleated mediacylinder; and, cylindrical length or pleat length. In general, aprincipal factor with respect to selecting media pleat depth, pleatlength, and pleat density, especially for barrier arrangements is thetotal surface area required for any given application or situation.

With respect to efficiency, principles vary with respect to the type ofmedia involved. For example, cellulose fiber or similar barrier media isgenerally varied, with respect to efficiency, by varying overall generalporosity or permeability. As explained in U.S. Pat. No. 5,423,892 and5,672,399, the efficiency of barrier media can be modified in someinstances by oiling the media and in others by applying, to a surface ofthe media, a deposit of relatively fine fibers, typically less than 5microns and in many instances submicron sized (average) fibers. Withrespect to fibrous depth media constructions, for example, dry laidfibrous media, as explained in U.S. Pat. No. 5,423,892, variablesconcerning efficiency include: percent solidity of the media, and howcompressed the media is within the construction involved; overallthickness or depth; and, fiber size.

With many engine air cleaner arrangements currently in the market, atleast one of two general types of sealing arrangements between theelement and the housing are used. One of these is a radially sealingarrangement. A variety of configurations of radially sealingarrangements are known, including: (1) the form available under theDonaldson trademark RadialSeal® from Donaldson Company of Minneapolis,Minn., and generally as described and characterized in European Patent0329659B1, incorporated herein by reference; (2) the type described byMann and Hummel in German Patent 4,241,586, and the corresponding(English language) published South African document 93/09129 publishedMay 8, 1994, incorporated herein by reference; and, (3) the typecharacterized by Fleetguard in U.S. Pat. No. 5,556,440 at column 10,lines 53-67 and FIG. 26, incorporated herein by reference. In general,with radially sealing arrangements, a seal is formed as a result offorces directed radially around a tube to which the element is sealed.

Another common type of sealing arrangement is generally referred to as“axial”. Axial systems are shown, for example, in U.S. Pat. Nos.3,078,650; 3,488,928; 4,20,783; 4,647,373; and 5,562,746 each of whichis incorporated herein by reference. In general, sealing forces for sucharrangements are directed along the longitudinal axis of the cylindricalair filter element that result from compression of a gasket between anend surface of the air filter and a surface of a housing in which theair filter is positioned, with the seal oriented circumferentiallyaround (or circumscribing) an air flow aperture or tube.

C. Typical System; Engine Air Intake

In FIG. 20, a schematic view of a system is shown generally at 120.System 20 is one example type of system in which air cleanerarrangements and constructions described herein is usable. In FIG. 20,equipment 121, such as a vehicle, having an engine 122 with some definedrated air flow demand is shown schematically. Equipment 121 may comprisea bus, an over the highway truck, an off-road vehicle, a tractor, ormarine application such as a power boat. Engine 122 powers equipment121, through use of an air, fuel mixture. In FIG. 20, air flow is showndrawn into engine 122 at an intake region 123. An optional turbo 124 isshown in phantom, as optionally boosting the air intake into the engine122. An air cleaner 125 having a media pack 126 is upstream of theengine 122 and turbo 124. In general, in operation, air is drawn in atarrow 127 into the air cleaner 125 and through media pack 126. There,particles and contaminants are removed from the air. The cleaned airflows downstream at arrow 128 into the intake 123. From there, the airflows into engine 122, to power equipment 121.

In engine systems, during operation of the engine and depending onconditions of power setting, load, external ambient temperature andother variables, the temperature, under the hood, typically is at least80° F. to 120° F., and often is in the range of 140° F. to 220° F. Whileunder normal operations the filter is often near ambient temperatures,during periods of low air flow or other non-standard operations thetemperature can reach 220° F. or more. Such temperatures can adverselyaffect the operating efficiency of the filter element. Regulations onemissions can increase the restriction on the engine exhaust, causingfurther increased temperatures. As explained below, constructing thefilter media in the form of a composite of a barrier media and at leasta single layer, and in some instances, multiple layers of “fine fiber”can improve the performance (the operating efficiency, in particular) ofthe filter element over prior art filter elements that are notconstructed from such media composites.

D. Example Air Cleaners

In reference now to FIGS. 21-24, a first embodiment of an air cleaner130 including a primary filter element 132 and a safety element 134 isdepicted. The air cleaner 130, in the particular embodiment depicted inFIGS. 21-24, is the type of air cleaner constructed for sealing by wayof a radially directed seal.

Turning first to the primary element 132, FIG. 22 illustrates theprimary element 132 in side, elevational view. The primary element 132depicted includes first and second opposite end caps 136, 138; an outersupport tube or liner 140; and a media pack 142 for filtering the air.The media pack 142 has first and second opposite ends 143, 144. At thefirst end 143 of the media pack 142, the first end cap 136 is secured tothe media pack 142; analogously, the second end 144 of the media pack142 is secured to the second end cap 138. In typical arrangements, thefirst and second end caps 136, 138 are molded from a compressiblematerial, such as polyurethane foam. In such arrangements, the mediapack 142 is bonded to the first and second end caps 136, 138 by pottingthe media in the polyurethane foam, before the polyurethane material hascured. Certain example materials for the first and second end caps 136,138 are described further below.

In preferred arrangements, the media pack 142 comprises a pleatedconstruction 146. By “pleated construction,” it is meant that the mediapack 142 has a series or plurality of folds or pleats, usually uniformlydistributed about the media pack 142.

In reference now to FIG. 21, it can be seen that the pleatedconstruction 146 is preferably in the form of a tube, preferablycylindrical, defining an open filter interior 148. The primary filterelement 132 forms a seal 150 with an air cleaner outlet tube 152 toinhibit the passage of air from bypassing the media pack 142 and flowingdirectly out through the outlet tube.

General principles of operation of the primary filter element 132 maynow be appreciated. In general, air to be filtered flows through themedia pack 142 from an external environment and into the open interior148. The media pack 148 operates to remove particulate matter from theair stream. From there, the air flows through the safety element 134 andinto an open interior 154 of the safety element. The cleaned air thenexits the air cleaner 130 through the flow conduit 156 formed by theoutlet tube 152. The seal 150 between the primary filter element 132 andthe outlet tube 152 prevents unfiltered air from bypassing the mediapack 142 and flowing directly through the flow conduit 156. A seal 158between the safety element 134 and the outlet tube 152 prevents air frombypassing the safety element 134. This is explained further below.

In reference now to FIG. 123, a preferred shape for the first end cap136 is utilized in order to obtain the seal 150. In particular, the endcap 136 includes an axial portion 160 and a radial portion 162. Theradial portion 162 circumscribes an end cap opening 164, which is in airflow communication with the open filter interior 148. The radial portion162 also acts as a sealing portion 166. The sealing portion 166 is madefrom a compressible material, such that it can be squeezed to deflecttoward the media pack 142 with hand pressure (less than 75 lbs.). Thesealing portion 166 preferably is in the form of a stepped construction168, which increases in thickness from the axial portion 160 of the endcap toward the interior 148. In particular, the stepped construction 168includes three steps 169, 170, 171 of increasing cross-sectionalthickness. This stepped construction 168 helps to allow the primaryelement 132 to more easily fit over the outlet tube 152 when mountingthe primary element 132 onto the outlet tube 152. Once seated properly,the sealing portion 166 forms the seal 150 with the outlet tube 152, andin particular, a radial seal 172. The radial seal 172 is formed bycompression of the sealing portion 66 between and against the outlettube 152 and an inner support tube or liner 174. The inner support liner174 extends between the first and second end caps 136, 138 and isusually potted within them and bonded thereto. The inner support tube174 is usually constructed analogously as the outer liner 140. As such,it is porous and air permeable, and can be constructed from expandedmetal.

The radial seal 162 is described in detail in U.S. Pat. No. 4,720,292B2, incorporated herein by reference.

The second end cap 138 is a closed end cap, in the embodiment depictedin FIGS. 22 and 23. By the term “closed,” it is meant that the secondend cap 138 is solid throughout and defines no apertures allowing forthe flow of fluid therethrough.

The sealing portion 166, and preferably the entire first end cap 136, isformed by a compressible material, preferably polyurethane, morepreferably polyurethane foam. In one usable embodiment, the materialcomprises polyurethane foam having an as-molded density of 14-22 lbs.per cubic inch. For a properly functioning radial seal 172, the sealingportion 166 needs to be substantially compressed when the primaryelement 132 is mounted on the outlet tube 152. In many preferredconstructions, it is compressed between about 15% and 40% (often about20-33%) of its thickness, in the thickest portion 171, to provide for astrong robust seal yet still be one that can result from handinstallation of the element 132 with forces on the order of 80 lbs. orless, preferably 75 lbs. or less, and generally 50-70 lbs. A usablematerial for the sealing portion 166 is described in U.S. Pat. No.5,613,992, incorporated herein by reference.

Turning now to FIG. 22 and the media pack 142, as described above, theair cleaner 130 when used in engine systems 120 may be subject totemperatures on the order of 80° F. to 220° F. The media pack 142 can bedesigned for improved overall efficiencies, as compared to prior art aircleaners. In general, the media pack 142 is arranged as a composite of asubstrate with a deposit of fine fibers thereon. In the particularembodiment illustrated, the substrate 180 is arranged in the pleatedconstruction 146. In many engine systems 120, the substrate 180comprises paper media or cellulose.

A particular preferred characteristic with respect to the substrate 180is permeability. In the embodiments utilized with an engine system 120,paper media having a permeability of at least 8 ft. per minute, andtypically and preferably about at least 12 ft. per minute, and mostpreferably within the range of 14 ft. per minute to 300 ft. per minute,prior to any treatment or deposit of fine fibers thereto will bepreferred. Preferably, a cellulose media having a basis weight of 50-80lbs./300 ft.² and a thickness of 0.010-0.018 inch is used.

The media composite includes a treatment, deposit, or coating of finefibers in order to increase efficiency under the high temperatureconditions of the engine system 120.

Turning now to FIG. 24, the safety element 134 is depicted. The safetyelement 134 includes first and second opposite end caps 190, 192; anouter support tube or liner 194; and a media pack 196 extending betweenand bonded to the first end cap 190 and second end cap 192. The mediapack 196 is depicted as a pleated construction 198 in a tubular orcylindrical shape defining the open interior 154.

The first end cap 190 is constructed as an open end cap, defining an airflow conduit 102 in gas flow communication with the open interior 154.The second end cap 192 is depicted as solid or closed end cap. Thesafety element 134 may optionally include an inner support tube or linerextending between the first and second end caps 190, 192 and between themedia pack 196 and the open interior 154.

The first end cap 190 includes a ring 104 of soft, pressable materialthereon, constructed and arranged to fit within the outlet tube 152 toseal against the inner surface 106 of the tube 152 in use. The safetyelement 134 is preferably sized and configured to fit underneath theprimary element 132, when mounted (see FIG. 21). The ring 104 preferablyis constructed of the same polyurethane foam described above for thesealing portion 166. A radial seal 108 is formed by compression of thematerial of the ring 104 between the media pack 196 and the outlet tube152.

In many preferred arrangements, the media pack 96 comprises a compositeincluding a cellulose substrate and a layer of fine fiber. The treatmentof fine fiber on the cellulose media of the pleated construction 98helps to increase operating efficiency or useful life in service withoutunduly increasing restriction, when utilized in environments such asengine system 120 with operating temperatures greater than 80° F. to140° F.

Attention is next directed to the embodiment of FIGS. 25-28. Depicted inFIGS. 25-28 is another air cleaner 115 that is usable with the enginesystem 120. With the exception of the preferred media arrangementdescribed in Section H, the general structure and geometry of the aircleaner 115 is described in U.S. Pat. No. 5,613,992, incorporated byreference herein.

The air cleaner 115 is the type generally described as a “reverse flow”air cleaner. By the term “reverse flow,” it is meant that air to befiltered generally enters the interior of the filter element and flowsoutwardly through the element into the volume between the air cleanerhousing and the element, and then is directed into the engine air intake123.

In FIG. 25, the air cleaner 115 is shown in side elevational view. Theair cleaner 115 includes a housing 116. The housing 116 generallyincludes an air intake hood 118 and a can 120. The can 120 includes anoutlet tube 122. The outlet tube 122 defines an aperture and directs thecleaned air from the housing 116 into the air intake region 23.

In FIG. 26, an exploded view of the air cleaner 115 is depicted. Afilter element 124 is shown removed from the housing 116. The filterelement 124 includes first and second opposite end caps 126, 128; anouter liner 130 extending between the first and second end caps 126,128; an inner liner 132 (FIG. 27) also extending the first and secondend caps 126, 128; and a media pack 134 (FIG. 27). In general, thefilter element 124 is removable and replaceable from the housing 116.Fasteners 136, 138 are shown in FIG. 26. It can be appreciated fromreviewing FIG. 26 that the air intake hood 118 can be removed from thecan 120 by disconnecting the fasteners 136, 138. Once the intake hood118 is removed from the can 120, it provides access to the filterelement 124. The filter element 124 may then be grasped and removed fromthe can 120. A replacement filter element may then be installed torefurbish the air cleaner 115.

The media pack 134, in the preferred embodiment, takes the form of atubular, usually cylindrical, pleated construction 140. The pleatedconstruction 140 defines an open filter interior 142 (FIGS. 27 and 28).The media is preferably formulated for high temperature (greater than140° F.) conditions.

Referring now to FIGS. 27 and 28, it can be seen how the filter element124 seals within the can 120. In FIG. 27, the first end cap 126 includesa sealing portion 144, which is compressible and deflectable. Thesealing portion 144 is at a radially inwardly part of the end cap 126.When the air inlet hood 118 is mounted over the element 124, the inlettube 146 of the hood 118 presses against the sealing portion 144 andcompresses the material of the end cap 126 against the inner liner 132.This forms a radial seal 148 between and against the inlet tube 146 andthe inner liner 142. Indeed, the construction and manner in which theradial seal 148 is formed is analogous to the sealing portion 66 andradial seal 72 in the embodiment of FIGS. 21-23. The sealing portion 144is preferably constructed out of the same polyurethane foam describedabove with respect to the sealing portion 66.

In FIG. 28, the bottom end cap 128 is shown forming another radial seal150 between and against the outer liner 130 and the wall 152 of the can120. In this case, the radial seal 150 is outwardly directed, somewhatanalogous to the manner in which the safety element 34 forms radial seal108. In FIG. 26, it can be seen that the end cap 128 includes a steppedconstruction 154 along the sealing portion 156, which corresponds to theoutside radial portion of the end cap 128. The sealing portion 156deflects and compresses when the filter element 124 is operablyinstalled in the can 120 and within the wall 152. In particular, thesealing portion 156 is compressed between and against the outer liner130 and the wall 152 to form the radial seal 150. Preferred end capmaterials include the same polyurethane foam described above for thesealing portion 144 and sealing portion 66.

In FIG. 28, it can also be appreciated that the second end cap 128defines an aperture 158. Preferably, the aperture 158 is centrallylocated. The aperture 158 allows for the drainage of moisture thatcollects in the filter interior 142. The end cap 128 is sloped to form afunnel surface 160, by sloping from the inner liner 132 to the centralaperture 158. This funnel surface 160 helps to direct collected moistureinto the aperture 158 and outside of the filter element 124.Periodically, a plug 162 may be removed from the can 120 to drain themoisture that collects in the pan 164.

Attention is now directed to FIG. 29, where another embodiment of an aircleaner 170 is depicted. Air cleaner 170 is usable in the engine system20. The structure and geometry is described, in general, in U.S. Pat.No. 4,020,783, which is incorporated herein by reference.

The air cleaner 170 is of the type generally referred to as an axialsealing air cleaner. The air cleaner 170 includes a housing 172, whichhas a body 174 and a removable cover 176. The cover 176 may beselectively removed from the body 174 by loosening the clamp arrangement178. This will expose and give access to the removable and replaceablefilter element 180. The body 174 includes a side or tangential inlettube 182 and an outlet tube 184. Dirty air to be cleaned before beingchanneled into the engine intake 23 flows through the inlet tube 182,through the filter element 180, and exits through the outlet tube 184.

The filter element 180 includes first and second end caps 186, 188; aninner and outer liner 190, 192 extending between the first and secondend caps 186, 188; and a media pack 194 bonded to the first and secondend caps 186, 188.

The media pack 194 is depicted as a tubular, preferably cylindricalpleated construction 196. The particular materials for the media in thepleated construction 196 is formulated for operation in a hightemperature environment such as the engine system 20.

In this embodiment, the first and second end caps 186, 188 areconstructed of sheet metal. The first end cap 186 supports an axiallydirected seal member 198. The air cleaner 170 includes a yokeconstruction 202, which includes a bolt 204 and a wing nut 206. The wingnut 206 can be rotated about the bolt 204 and cause axially directedforces between the end wall 208 of the body 174 and the seal member 198to form an axial seal 210 between and against the first end cap 186 andthe wall 208 of the body 174.

The air cleaner 170 also includes a safety element 212 operablyinstalled therein. Other features of the housing 172 include a bafflemember 214 in order to deflect air taken in through the inlet tube 182.

In operation, air to be filtered flows through the inlet tube 182, isdeflected by the baffle member 214, and swirls within the housing 172.The swirling action causes the heavier dust particles to drop by gravityto the bottom cover 176. The air to be cleaned then flows through themedia pack 194 and into the open filter interior 216. It then flowsthrough the safety element 212 and through the porous yoke construction202, before it finally passes out through the outlet tube 184. Thecleaned air is then directed to an intake, such as air intake 123 ofengine 122.

In FIGS. 30 and 31, another air cleaner 220 is depicted that is usablein the engine system 120. The structure and geometry of air cleaner 220is described in U.S. Pat. No. 5,112,372 and U.S. Pat. No. 4,350,509,each of which is incorporated by reference herein.

The air cleaner 220 includes a housing 222 that is preferably integralwith a filter element 224. As such, the filter element 224 includesfirst and second end caps 226, 228 that is integral with the housing222. The filter element 224 includes a media pack 230 secured to thefirst and second end caps 226, 228 and extending therebetween. The mediapack 230 comprises a tubular, preferably cylindrical, pleatedconstruction 232 defining an open filter interior 234. The pleatedconstruction 232 is preferably made from media formulations as describedbelow which are particularly adapted for high temperature applications.

The air cleaner 220 also includes a resonator 236 oriented within theopen interior 234.

FIG. 31 is an end view of the air cleaner 220. To provide a source ofintake air for the air cleaner 220, at least one aperture is formed inone of the end caps 226, 228. In the particular one illustrated in FIG.31, a plurality of apertures 238 are defined by the first end cap 226 toallow air to enter the air cleaner 220 and occupy the volume 240 betweenthe housing wall 242 and the media pack 230.

An outlet tube 244 projects from the first end cap 226 and allows forthe exit of cleaned air from the air cleaner 220.

In operation, air to be filtered enters the air cleaner 220 through theapertures 238 and flows into the volume 240. The air then flows throughthe pleated construction 232 and into the open filter interior 234. Thesound is attenuated by the resonator 236, and the cleaned air flowsthrough the outlet tube 244 to exit the air cleaner 220. From there, theair is directed to an air intake, such as intake region 23 of system 20.

Another embodiment of a filter element is shown in FIGS. 32 and 33. Inthis embodiment, the filter element 250 takes the form of a panel filter252. The panel filter element 252 includes a media pack 254 in the formof a pleated construction 256. As can be seen from review of FIGS. 32and 33, the pleated construction 256 forms generally a flat panel with aplurality of pleats 258.

The panel filter construction 252 has an outer perimeter gasket member260 in order to form a seal with a cooperating housing.

The media pack 254 includes a media construction that is speciallyformulated for operation in high temperature conditions, such as inengine system 20. The panel filter element 252 with the speciallyformulated media pack 254 is also usable in systems such as fluidcompressors.

E. Typical System; Fluid Compressor

A fluid compressor is shown schematically in FIG. 34 at 265. The fluidcompressor 265 includes an air cleaner 268 with a filter element 270.One usable filter element 270 is the panel filter construction 252(FIGS. 32 and 33). The fluid compressor 265 includes a frame 272 thatencloses a crankshaft 274 and piston connecting rods for driving pistonmembers in a conventional manner through a cylinder 276. A valve plate278 is sandwiched between the top of the cylinder 276 and a compressorhead 280. In general, the compressor 265 is a reciprocating, piston typecompressor well known to one skilled in the art. Air to be compressedenters the compressor 265 in the direction shown at arrow 282. The airflows through the air cleaner 268, where particulates are removed by thefilter element 270. The cleaned air then flows into the head 280, andthe compressor 265 operates to compress the air.

Compressors 265 are sometimes used in environments that are hightemperature (greater than 140° F.).

F. Typical Media Sizes

For the filter elements described herein, each preferably includes apleated construction. In these types of applications, the pleat lengthis at least 6 inches, no greater than 50 inches, and may be 8-40 inches.The pleat depth is usually at least 0.5 inches, no greater than 12inches, and may be 1-6 inches.

For tubular constructions, the outer diameter of the pleatedconstruction is usually at least 4 inches, no greater than 50 inches,and may typically be 6-30 inches. For panel filter constructions, thereare usually at least 40 pleats, no greater than 200 pleats, andtypically 50-100 pleats.

G. Typical System; Tank with Gas Turbine

In FIG. 35, 36 and 37, an M1 tank filter is shown. The M1 tank is gasturbine powered. The turbine engine is generally located under armorplating. The gas turbine engine requires large amounts of ambient airfor operation. The ambient air should be filtered for removal ofparticulate matter therein before it is directed into the gas turbineengine. The tank includes an air inlet to take in air for the turbineengine. The tank includes an air cleaner under the armor plating at. Thetank also includes a scavenger outlet for exhaust of particulatematerial from the air cleaner.

H. Example Air Cleaner for Tank

In FIGS. 35, 36 and 37, one example air cleaner 330 useable in the tankis illustrated. The air cleaner 330 includes a plurality of filterelements 332 positioned within a filter housing 334. For the particulararrangement shown, each filter element 332 includes a V-shaped mediapack 336. In the one shown, the housing 334 is sized to operably receive3 V-shaped media packs 336 therein, aligned side by side but spacedapart, during use and assembly.

With the exception of the preferred media formulation described below inSection H, the air cleaner 330, together with the system for the tank isdescribed in U.S. Pat. No. 5,575,826, which is incorporated by referenceherein. Further, other than the preferred media formulation discussed inSection H below, each of the V-shaped media packs 336 is described inU.S. Pat. No. 4,364,751, which is incorporated herein by reference.

In reference to FIGS. 35, 36 and 37, each media pack 336 includes aframe 338 with end caps 340, 341. For the embodiment shown, eachV-shaped media pack 336 includes 2 panels 342, 343 oriented in aV-shaped configuration with an internal channel or space 345 positionedtherebetween. For the arrangement utilized, each internal space 345 isdivided into 3 compartments by internal baffles 346, 347.

Panels 342, 343 are each occupied by pleated filter media 348. Thepleated media 348 includes cellulose media treated with fine fiber. Thistype of media helps to improve the efficiency of the air cleaner 330 inhigh temperature environments, such as those that the tank experiences.

In FIGS. 35, 36 and 37, the filter housing 334 includes an inlet 350,and an outlet 352. Each of the 3 media packs 336 can be seen within thehousing 334, arranged side-by-side. A partition 354 provides a surfacein which each of the media packs 336 seals against in order to separatethe dirty air side 356 from the clean air side 357. In particular, eachof the media packs 336 includes a gasket 358 that compresses against thepartition 354 and helps to inhibit airflow from the dirty side 356 frombypassing the media 348 and flowing directly into the clean side 357.The partition 354 includes airflow apertures 360 in order to allow forthe flow of cleaned air from the volume or space 345 and into the cleanair side 357.

Operation of the V-shaped media packs 336 is generally as follows. Theair enters the air cleaner 330 through the inlet 352 in the housing 334.The air enters the panels 342, 343 and is directed toward the internalspace 345. Particulate material is left on the exterior surfaces of thepanels 342, 343 (on the side or surface of the panel directed away fromthe internal space 345) or on the developing filter cake. The filteredair occupies the internal volume 345 and flows through the ports orapertures 360 and into the clean air side 357. From there, the air flowsout through the outlet 352 and is directed to the gas turbine.

The air cleaner 330 also includes a pulse jet system for cleaning. Ingeneral, such a system provides for a selected jet pulse of air directedbackwards through the filter panels 342, 343. By backwards in thiscontext, it is meant that the pulse jet is directed opposite to normalair flow (i.e., filtering air flow) during filtering of ambient air. Forthe arrangements shown, this direction would be with the pulse jet aimedinto space 345 to ultimately direct air through the panels 342, 343 andthen outwardly from the surface of the pleated media 348.

In FIG. 35, a pulse jet cleaning systems includes 3 valves 360 connectedto stand pipes 362, which are in air flow communication with compressedair. Each of the valves 360 connect with diffusers nozzles 364, that arepositioned so that the nozzles are directed centrally into the chambersor spaces 345.

Periodically, all or selected ones of the pulse jet valves 360 may beopened to release a pulse or jet of air into an associated portion ofthe internal space 345 of the V-shaped media pack 336. This jet pulsewill tend to flush dirt, dust, or the like off of the panels 342, 343.The particulate material will tend to disburse into the regionimmediately surrounding the panel from which it is flushed.

I. Preferred Media Formulations

For each of the filter elements described herein, the media packsinclude a media composite, which includes a substrate at least partiallytreated or coated or covered by a layer of non-woven fibers.

The fine fibers that comprise the micro- or nanofiber containing layerof the invention can be fiber and can have a diameter of about 0.001 to10 micron, preferably 0.05 to 0.5 micron. In certain applications, thefiber can be sized to 0.001 to 2 microns, 0.01 to 5 microns and 0.05 to10 microns. The thickness of the typical fine fiber filtration layerranges from about 1 to 100 times the fiber diameter with a basis weightranging from about 0.01 to 240 micrograms-cm⁻².

Fluid streams such as air and gas streams often carry particulatematerial therein. The removal of some or all of the particulate materialfrom the fluid stream is needed. For example, air intake streams to thecabins of motorized vehicles, air in computer disk drives, HVAC air,clean room ventilation and applications using filter bags, barrierfabrics, woven materials, air to engines for motorized vehicles, or topower generation equipment; gas streams directed to gas turbines; and,air streams to various combustion furnaces, often include particulatematerial therein. In the case of cabin air filters it is desirable toremove the particulate matter for comfort of the passengers and/or foraesthetics. With respect to air and gas intake streams to engines, gasturbines and combustion furnaces, it is desirable to remove theparticulate material because particulate can cause substantial damage tothe internal workings to the various mechanisms involved. In otherinstances, production gases or off gases from industrial processes orengines may contain particulate material therein. Before such gases canbe, or should be, discharged through various downstream equipment to theatmosphere, it may be desirable to obtain a substantial removal ofparticulate material from those streams.

A general understanding of some of the basic principles and problems ofair filter design can be understood by consideration of the followingtypes of filter media: surface loading media; and, depth media. Each ofthese types of media has been well studied, and each has been widelyutilized. Certain principles relating to them are described, forexample, in U.S. Pat. Nos. 5,082,476; 5,238,474; and 5,364,456. Thecomplete disclosures of these three patents are incorporated herein byreference.

The “lifetime” of a filter is typically defined according to a selectedlimiting pressure drop across the filter. The pressure buildup acrossthe filter defines the lifetime at a defined level for that applicationor design. Since this buildup of pressure is a result of load, forsystems of equal efficiency a longer life is typically directlyassociated with higher capacity. Efficiency is the propensity of themedia to trap, rather than pass, particulates. It should be apparentthat typically the more efficient a filter media is at removingparticulates from a gas flow stream, in general the more rapidly thefilter media will approach the “lifetime” pressure differential(assuming other variables to be held constant).

Paper filter elements are widely used forms of surface loading media. Ingeneral, paper elements comprise dense mats of cellulose, synthetic orother fibers oriented across a gas stream carrying particulate material.The paper is generally constructed to be permeable to the gas flow, andto also have a sufficiently fine pore size and appropriate porosity toinhibit the passage of particles greater than a selected sizetherethrough. As the gases (fluids) pass through the filter paper, theupstream side of the filter paper operates through diffusion andinterception to capture and retain selected sized particles from the gas(fluid) stream. The particles are collected as a dust cake on theupstream side of the filter paper. In time, the dust cake also begins tooperate as a filter, increasing efficiency. This is sometimes referredto as “seasoning,” i.e. development of an efficiency greater thaninitial efficiency.

A simple filter design such as that described above is subject to atleast two types of problems. First, a relatively simple flaw, i.e.rupture of the paper, results in failure of the system. Secondly,particulate material rapidly builds up on the upstream side of thefilter, as a thin dust cake or layer, increasing the pressure drop.Various methods have been applied to increase the “lifetime” ofsurface-loaded filter systems, such as paper filters. One method is toprovide the media in a pleated construction, so that the surface area ofmedia encountered by the gas flow stream is increased relative to aflat, non-pleated construction. While this increases filter lifetime, itis still substantially limited. For this reason, surface loaded mediahas primarily found use in applications wherein relatively lowvelocities through the filter media are involved, generally not higherthan about 20-30 feet per minute and typically on the order of about 10feet per minute or less. The term “velocity” in this context is theaverage velocity through the media (i.e. flow volume per media area).

In general, as air flow velocity is increased through a pleated papermedia, filter life is decreased by a factor proportional to the squareof the velocity. Thus, when a pleated paper, surface loaded, filtersystem is used as a particulate filter for a system that requiressubstantial flows of air, a relatively large surface area for the filtermedia is needed. For example, a typical cylindrical pleated paper filterelement of an over-the-highway diesel truck will be about 9-15 inches indiameter and about 12-24 inches long, with pleats about 1-2 inches deep.Thus, the filtering surface area of media (one side) is typically 30 to300 square feet.

In many applications, especially those involving relatively high flowrates, an alternative type of filter media, sometimes generally referredto as “depth” media, is used. A typical depth media comprises arelatively thick tangle of fibrous material. Depth media is generallydefined in terms of its porosity, density or percent solids content. Forexample, a 2-3% solidity media would be a depth media mat of fibersarranged such that approximately 2-3% of the overall volume comprisesfibrous materials (solids), the remainder being air or gas space.

Another useful parameter for defining depth media is fiber diameter. Ifpercent solidity is held constant, but fiber diameter (size) is reduced,pore size or interfiber space is reduced; i.e. the filter becomes moreefficient and will more effectively trap smaller particles.

A typical conventional depth media filter is a deep, relatively constant(or uniform) density, media, i.e. a system in which the solidity of thedepth media remains substantially constant throughout its thickness. By“substantially constant” in this context, it is meant that onlyrelatively minor fluctuations in density, if any, are found throughoutthe depth of the media. Such fluctuations, for example, may result froma slight compression of an outer engaged surface, by a container inwhich the filter media is positioned.

Gradient density depth media arrangements have been developed. some sucharrangements are described, for example, in U.S. Pat. Nos. 4,082,476;5,238,474; and 5,364,456. In general, a depth media arrangement can bedesigned to provide “loading” of particulate materials substantiallythroughout its volume or depth. Thus, such arrangements can be designedto load with a higher amount of particulate material, relative tosurface loaded systems, when full filter lifetime is reached. However,in general the tradeoff for such arrangements has been efficiency,since, for substantial loading, a relatively low solidity media isdesired. Gradient density systems such as those in the patents referredto above, have been designed to provide for substantial efficiency andlonger life. In some instances, surface loading media is utilized as a“polish” filter in such arrangements.

A filter media construction according to the present invention includesa first layer of permeable coarse fibrous media or substrate having afirst surface. A first layer of fine fiber media is secured to the firstsurface of the first layer of permeable coarse fibrous media. Preferablythe first layer of permeable coarse fibrous material comprises fibershaving an average diameter of at least 10 microns, typically andpreferably about 12 (or 14) to 30 microns. Also preferably the firstlayer of permeable coarse fibrous material comprises a media having abasis weight of no greater than about 200 grams/meter², preferably about0.50 to 150 g/m², and most preferably at least 8 g/m². Preferably thefirst layer of permeable coarse fibrous media is at least 0.0005 inch(12 microns) thick, and typically 0.0006 to 0.02 (15 to 500 microns)thick and preferably is about 0.001 to 0.030 inch (25-800 microns)thick.

In preferred arrangements, the first layer of permeable coarse fibrousmaterial comprises a material which, if evaluated separately from aremainder of the construction by the Frazier permeability test, wouldexhibit a permeability of at least 1 meter(s)/min, and typically andpreferably about 2-900 meters/min. Herein when reference is made toefficiency, unless otherwise specified, reference is meant to efficiencywhen measured according to ASTM-1215-89, with 0.7811 monodispersepolystyrene spherical particles, at 20 fpm (6.1 meters/min) as describedherein.

Preferably the layer of fine fiber material secured to the first surfaceof the layer of permeable coarse fibrous media is a layer of nano- andmicrofiber media wherein the fibers have average fiber diameters of nogreater than about 2 to 10 microns, generally and preferably no greaterthan about 5 microns, and typically and preferably have at least somefiber with diameters smaller than 0.5 micron and within the range ofabout 0.05 to 0.5 micron. Also, preferably the first layer of fine fibermaterial secured to the first surface of the first layer of permeablecoarse fibrous material has an overall thickness that is no greater thanabout 30 microns, more preferably no more than 20 microns, mostpreferably no greater than about 10 microns, and typically andpreferably that is within a thickness of about 1-8 times (and morepreferably no more than 5 times) the fine fiber average diameter of thelayer.

Certain preferred arrangements according to the present inventioninclude filter media as generally defined, in an overall filterconstruction. Some preferred arrangements for such use comprise themedia arranged in a cylindrical, pleated configuration with the pleatsextending generally longitudinally, i.e. in the same direction as alongitudinal axis of the cylindrical pattern. For such arrangements, themedia may be imbedded in end caps, as with conventional filters. Sucharrangements may include upstream liners and downstream liners ifdesired, for typical conventional purposes.

In some applications, media according to the present invention may beused in conjunction with other types of media, for example conventionalmedia, to improve overall filtering performance or lifetime. Forexample, media according to the present invention may be laminated toconventional media, be utilized in stack arrangements; or beincorporated (an integral feature) into media structures including oneor more regions of conventional media. It may be used upstream of suchmedia, for good load; and/or, it may be used downstream fromconventional media, as a high efficiency polishing filter.

Certain arrangements according to the present invention may also beutilized in liquid filter systems, i.e. wherein the particulate materialto be filtered is carried in a liquid. Also, certain arrangementsaccording to the present invention may be used in mist collectors, forexample arrangements for filtering fine mists from air.

According to the present invention, methods are provided for filtering.The methods generally involve utilization of media as described toadvantage, for filtering. As will be seen from the descriptions andexamples below, media according to the present invention can bespecifically configured and constructed to provide relatively long lifein relatively efficient systems, to advantage.

Various filter designs are shown in patents disclosing and claimingvarious aspects of filter structure and structures used with the filtermaterials. Engel et al., U.S. Pat. No. 4,720,292, disclose a radial sealdesign for a filter assembly having a generally cylindrical filterelement design, the filter element being sealed by a relatively soft,rubber-like end cap having a cylindrical, radially inwardly facingsurface. Kahlbaugh et al., U.S. Pat. No. 5,082,476, disclose a filterdesign using a depth media comprising a foam substrate with pleatedcomponents combined with the microfiber materials of the invention.Stifelman et al., U.S. Pat. No. 5,104,537, relate to a filter structureuseful for filtering liquid media. Liquid is entrained into the filterhousing, passes through the exterior of the filter into an interiorannular core and then returns to active use in the structure. Suchfilters are highly useful for filtering hydraulic fluids. Engel et al.,U.S. Pat. No. 5,613,992, show a typical diesel engine air intake filterstructure. The structure obtains air from the external aspect of thehousing that may or may not contain entrained moisture. The air passesthrough the filter while the moisture can pass to the bottom of thehousing and can drain from the housing. Gillingham et al., U.S. Pat. No.5,820,646, disclose a Z filter structure that uses a specific pleatedfilter design involving plugged passages that require a fluid stream topass through at least one layer of filter media in a “Z” shaped path toobtain proper filtering performance. The filter media formed into thepleated Z shaped format can contain the fine fiber media of theinvention. Glen et al., U.S. Pat. No. 5,853,442, disclose a bag housestructure having filter elements that can contain the fine fiberstructures of the invention. Berkhoel et al., U.S. Pat. No. 5,954,849,show a dust collector structure useful in processing typically airhaving large dust loads to filter dust from an air stream afterprocessing a workpiece generates a significant dust load in anenvironmental air. Lastly, Gillingham, U.S. Design Patent No. 425,189,discloses a panel filter using the Z filter design.

The foregoing general description of the various aspects of thepolymeric materials of the invention, the fine fiber materials of theinvention including both microfibers and nanofibers and the constructionof useful filter structures from the fine fiber materials of theinvention provides an understanding of the general technologicalprinciples of the operation of the invention. The specific exemplarymaterials set forth below are examples of materials that can be used inthe formation of the fine fiber materials of the invention and thefollowing materials disclose a best mode. These exemplary materials weremanufactured with the following characteristics and process conditionsin mind. Electrospinning small diameter fiber less than 10 micron isobtained using an electrostatic force from a strong electric fieldacting as a pulling force to stretch a polymer jet into a very finefilament. A polymer melt can be used in the electrospinning process,however, fibers smaller than 1 micron are best made from polymersolution. As the polymer mass is drawn down to smaller diameter, solventevaporates and contributes to the reduction of fiber size. Choice ofsolvent is critical for several reasons. If solvent dries too quickly,then fibers tends to be flat and large in diameter. If the solvent driestoo slowly, solvent will redissolve the formed fibers. Thereforematching drying rate and fiber formation is critical. At high productionrates, large quantities of exhaust air flow helps to prevent a flammableatmosphere, and to reduce the risk of fire. A solvent that is notcombustible is helpful. In a production environment the processingequipment will require occasional cleaning. Safe low toxicity solventsminimize worker exposure to hazardous chemicals. Electrostatic spinningcan be done at a flow rate of 1.5 ml/min per emitter, a target distanceof 8 inches, an emitter voltage of 88 kV, an emitter rpm of 200 and arelative humidity of 45%.

The choice of polymer system is important for a given application. Forpulse cleaning application, an extremely thin layer of microfiber canhelp to minimize pressure loss and provide an outer surface for particlecapture and release. A thin layer of fibers of less than 2-microndiameter, preferably less than 0.3-micron diameter is preferred. Goodadhesion between microfiber or nanofiber and substrates upon which themicrofibers or nanofibers are deposited is important. When filters aremade of composites of substrate and thin layer of micro- and nanofibers,such composite makes an excellent filter medium for self-cleaningapplication. Cleaning the surface by back pulsing repeatedly rejuvenatesthe filter medium. As a great force is exerted on the surface, finefiber with poor adhesion to substrates can delaminate upon a back pulsethat passes from the interior of a filter through a substrate to themicro fiber. Therefore, good cohesion between micro fibers and adhesionbetween substrate fibers and electrospun fibers is critical forsuccessful use.

Products that meet the above requirements can be obtained using fibersmade from different polymer materials. Small fibers with good adhesionproperties can be made from such polymers like polyvinylidene chloride,poly vinyl alcohol and polymers and copolymers comprising various nylonssuch as nylon 6, nylon 4,6; nylon 6,6; nylon 6,10 and copolymersthereof. Excellent fibers can be made from PVDF, but to makesufficiently small fiber diameters requires chlorinated solvents. Nylon6, Nylon 66 and Nylon 6,10 can be electrospun. But, solvents such asformic acid, m-cresol, tri-fluoro ethanol, hexafluoro isopropanol areeither difficult to handle or very expensive. Preferred solvents includewater, ethanol, isopropanol, acetone and N-methyl pyrrolidone due totheir low toxicity. Polymers compatible with such solvent systems havebeen extensively evaluated. We have found that fibers made from PVC,PVDC, polystyrene, polyacrylonitrile, PMMA, PVDF require additionaladhesion means to attain structural properties. We also found that whenpolymers are dissolved in water, ethanol, isopropanol, acetone, methanoland mixtures thereof and successfully made into fibers, they haveexcellent adhesion to the substrate, thereby making an excellent filtermedium for self-cleaning application. Self-cleaning via back air pulseor twist is useful when filer medium is used for very high dustconcentration. Fibers from alcohol soluble polyamides and poly(vinylalcohol)s have been used successfully in such applications. Examples ofalcohol soluble polyamides include Macromelt 6238, 6239, and 6900 fromHenkel, Elvamide 8061 and 8063 from duPont and SVP 637 and 651 fromShakespeare Monofilament Company. Another group of alcohol solublepolyamide is type 8 nylon, alkoxy alkyl modifies nylon 66 (Ref. Page447, Nylon Plastics handbook, Melvin Kohan ed. Hanser Publisher, NewYork, 1995). Examples of poly(vinyl alcohol) include PVA-217, 224 fromKuraray, Japan and Vinol 540 from Air Products and Chemical Company.

Experimental

The following materials were produced using the following electrospinprocess conditions.

The following materials were spun using either a rotating emitter systemor a capillary needle system. Both were found to produce substantiallythe same fibrous materials.

The flow rate was 1.5 mil/min per emitter, a target distance of 8inches, an emitter voltage of 88 kV, a relative humidity of 45%, and forthe rotating emitter an rpm of 35.

EXAMPLE 1 Effect of Fiber Size

Fine fiber samples were prepared from a copolymer of nylon 6, 66, 610nylon copolymer resin (SVP-651) was analyzed for molecular weight by theend group titration. (J. E. Walz and G. B. Taylor, determination of themolecular weight of nylon, Anal. Chem. Vol. 19, Number 7, pp 448-450(1947). Number average molecular weight was between 21,500 and 24,800.The composition was estimated by the phase diagram of melt temperatureof three component nylon, nylon 6 about 45%, nylon 66 about 20% andnylon 610 about 25%. (Page 286, Nylon Plastics Handbook, Melvin Kohaned. Hanser Publisher, New York (1995)). Reported physical properties ofSVP 651 resin are:

Property ASTM Method Units Typical Value Specific Gravity D-792 —  1.08Water Absorption D-570 %   2.5 (24 hr immersion) Hardness D-240 Shore D 65 Melting Point DSC ° C. (° F.) 154 (309) Tensile Strength D-638 MPa(kpsi)  50 (7.3) @ Yield Elongation at Break D-638 % 350 FlexuralModulus D-790 MPa (kpsi) 180 (26) Volume Resistivity D-257 ohm-cm  10¹²to produce fiber of 0.23 and 0.45 micron in diameter. Samples weresoaked in room temperature water, air-dried and its efficiency wasmeasured. Bigger fiber takes longer time to degrade and the level ofdegradation was less as can be seen in the plot of FIG. 12. Whilewishing not to be limited by certain theory, it appears that smallerfibers with a higher surface/volume ratio are more susceptible todegradation due to environmental effects. However, bigger fibers do notmake as efficient filter medium.

EXAMPLE 2 Cross-linking of Nylon Fibers with Phenolic Resin and EpoxyResin

In order to improve chemical resistance of fibers, chemicalcross-linking of nylon fibers was attempted. Copolyamide (nylon 6, 66,610) described earlier is mixed with phenolic resin, identified asGeorgia Pacific 5137 and spun into fiber. Nylon:Phenolic Resin ratio andits melt temperature of blends are shown here;

Composition Melting Temperature (F.°) Polyamide:Phenolic = 100:0 150Polyamide:Phenolic = 80:20 110 Polyamide:Phenolic = 65:35 94Polyamide:Phenolic = 50:50 65

We were able to produce comparable fiber from the blends. The 50:50blend could not be cross-linked via heat as the fibrous structure wasdestroyed. Heating 65:35 blend below 90 degree C. for 12 hours improvesthe chemical resistance of the resultant fibers to resist dissolution inalcohol. Blends of polyamide with epoxy resin, such Epon 828 from Shelland Epi-Rez 510 can be used.

EXAMPLE 3 Surface modification though Fluoro Additive (Scotchgard®)Repellant

Alcohol miscible Scotchgard® FC-430 and 431 from 3M Company were addedto polyamide before spinning. Add-on amount was 10% of solids. Additionof Scotchgard did not hinder fiber formation. THC bench shows thatScotchgard-like high molecular weight repellant finish did not improvewater resistance. Scotchgard added samples were heated at 300° F. for 10minutes as suggested by manufacturer.

EXAMPLE 4 Modification with Coupling Agents

Polymeric films were cast from polyamides with tinanate coupling agentsfrom Kenrich Petrochemicals, Inc. They include isopropyl triisostearoyltitanate (KR TTS), neopentyl (diallyl) oxytri (dioctyl) phosphatotitanate (LICA12), neopentyl (dially) oxy, tri(N-ethylene diamino)ethylzirconate (NZ44). Cast films were soaked in boiling water. Controlsample without coupling agent loses its strength immediately, whilecoupling agent added samples maintained its form for up to ten minutes.These coupling agents added samples were spun into fiber (0.2 micronfiber).

EXAMPLE 5 Modification with Low Molecular Weight P-Tert-Butyl PhenolPolymer

Oligomers of para-tert-butyl phenol, molecular weight range 400 to 1100,was purchased from Enzymol International, Columbus, Ohio. These lowmolecular weight polymers are soluble in low alcohols, such as ethanol,isopropanol and butanol. These polymers were added to co-polyamidedescribed earlier and electrospun into 0.2 micron fibers without adverseconsequences. Some polymers and additives hinder the electrospinningprocess. Unlike the conventional phenolic resin described in Example 2,we have found that this group of polymers does not interfere with fiberforming process.

We have found that this group of additive protects fine fibers from wetenvironment as see in the plot. FIGS. 13-16 show that oligomers providea very good protection at 140° F., 100% humidity and the performance isnot very good at 160° F. We have added this additive between 5% and 15%of polymer used. We have found that they are equally effectiveprotecting fibers from exposure to high humidity at 140° F. We have alsofound out that performance is enhanced when the fibers are subjected to150° C. for short period of time.

Table 1 shows the effect of temperature and time exposure of 10% add-onto polyamide fibers.

TABLE 1 Efficiency Retained (%) After 140 deg. F. Soak: Heating TimeTemperature 1 min 3 min 10 min 150 C.° 98.9 98.8 98.5 98.8 98.9 98.8 130C.° 95.4 98.7 99.8 96.7 98.6 99.6 110 C.° 82.8 90.5 91.7 86.2 90.9 85.7

This was a surprising result. We saw dramatic improvement in waterresistance with this family of additives. In order to understand howthis group of additive works, we have analyzed the fine fiber mat withsurface analysis techniques called ESCA. 10% add-on samples shown inTable 1 were analyzed with ESCA at the University of Minnesota with theresults shown in Table 2.

TABLE 2 Surface Composition (Polymer:Additive Ratio) Heating TimeTemperature 1 min 3 min 10 min 150 C.° 40:60 40:60 50:50 130 C.° 60:4056:44 62:82 110 C.° 63:37 64:36 59:41 No Heat 77:23

Initially, it did not seem to make sense to find surface concentrationof additive more than twice of bulk concentration. However, we believethat this can be explained by the molecular weight of the additives.Molecular weight of the additive of about 600 is much smaller than thatof host fiber forming polymer. As they are smaller in size, they canmove along evaporating solvent molecules. Thus, we achieve highersurface concentration of additives. Further treatment increases thesurface concentration of the protective additive. However, at 10 minexposure, 150° F., did not increase concentration. This may be anindication that mixing of two components of copolyamide and oligomermolecules is happening as long chain polymer has a time to move around.What this analysis has taught us is that proper selection of posttreatment time and temperature can enhance performance, while too longexposure could have a negative influence.

We further examined the surface of these additive laden microfibersusing techniques called Time of Flight SIMS. This technique involvesbombarding the subject with electrons and observes what is coming fromthe surface. The samples without additives show organic nitrogen speciesare coming off upon bombardment with electron. This is an indicationthat polyamide species are broken off. It also shows presence of smallquantity of impurities, such as sodium and silicone. Samples withadditive without heat treatment (23% additive concentration on surface)show a dominant species of t-butyl fragment, and small but unambiguouspeaks observed peaks observed for the polyamides. Also observed are highmass peaks with mass differences of 148 amu, corresponding to t-butylphenol. For the sample treated at 10 min at 150° C. (50% surfaceadditive concentration by ESCA analysis), inspection shows dominance oft-butyl fragments and trace, if at all, of peaks for polyamide. It doesnot show peaks associated with whole t-butyl phenol and its polymers. Italso shows a peak associated with C₂H₃O fragments.

The ToF SIMS analysis shows us that bare polyamide fibers will give offbroken nitrogen fragment from exposed polymer chain and contaminants onthe surface with ion bombardment. Additive without heat treatment showsincomplete coverage, indicating that additives do not cover portions ofsurface. The t-butyl oligomers are loosely organized on the surface.When ion beam hits the surface, whole molecules can come off along withlabile t-butyl fragment. Additive with heat treatment promotes completecoverage on the surface. In addition, the molecules are tightly arrangedso that only labile fragments such as t-butyl-, and possibly CH═CH—OH,are coming off and the whole molecules of t-butyl phenol are not comingoff. ESCA and ToF SIMS look at different depths of surface. ESCA looksat deeper surface up to 100 Angstrom while ToF SIMS only looks at10-Angstrom depth. These analyses agree.

EXAMPLE 6 Development of Surface Coated Interpolymer

Type 8 Nylon was originally developed to prepare soluble andcrosslinkable resin for coating and adhesive application. This type ofpolymer is made by the reaction of polyamide 66 with formaldehyde andalcohol in the presence of acid. (Ref. Cairns, T. L.; Foster, H. D.;Larcher, A. W.; Schneider, A. K.; Schreiber, R. S. J. Am. Chem. Soc.1949, 71, 651). This type of polymer can be electrospun and can becross-linked. However, formation of fiber from this polymer is inferiorto copolyamides and crosslinking can be tricky.

In order to prepare type 8 nylon, 10-gallon high-pressure reactor wascharged with the following ratio:

Nylon 66 (duPont Zytel 101)   10 pounds Methanol 15.1 pounds Water  2.0pounds Formaldehyde 12.0 pounds

The reactor is then flushed with nitrogen and is heated to at least 135°C. under pressure. When the desired temperature was reached, smallquantity of acid was added as catalyst. Acidic catalysts includetrifluoroacetic acid, formic acid, toluene sulfonic acid, maleic acid,maleic anhydride, phthalic acid, phthalic anhydride, phosphoric acid,citric acid and mixtures thereof. Nafion® polymer can also be used as acatalyst. After addition of catalyst, reaction proceeds up to 30minutes. Viscous homogeneous polymer solution is formed at this stage.After the specified reaction time, the content of the high pressurevessel is transferred to a bath containing methanol, water and base,like ammonium hydroxide or sodium hydroxide to shortstop the reaction.After the solution is sufficiently quenched, the solution isprecipitated in deionized water. Fluffy granules of polymer are formed.Polymer granules are then centrifuged and vacuum dried. This polymer issoluble in, methanol, ethanol, propanol, butanol and their mixtures withwater of varying proportion. They are also soluble in blends ofdifferent alcohols.

Thus formed alkoxy alkyl modified type 8 polyamide is dissolved inethanol/water mixture. Polymer solution is electrospun in a mannerdescribed in Barris U.S. Pat. No. 4,650,516. Polymer solution viscositytends to increase with time. It is generally known that polymerviscosity has a great influence in determining fiber sizes. Thus, it isdifficult to control the process in commercial scale, continuousproduction. Furthermore, under same conditions, type 8 polyamides do notform microfibers as efficiently as copolyamides. However, when thesolution is prepared with addition of acidic catalyst, such as toluenesulfonic acid, maleic anhydride, trifluoro methane sulfonic acid, citricacid, ascorbic acid and the like, and fiber mats are carefullyheat-treated after fiber formation, the resultant fiber has a very goodchemical resistance. (FIG. 13). Care must be taken during thecrosslinking stage, so that one does not destroy fibrous structure.

We have found a surprising result when type 8 polyamide (polymer B) isblended with alcohol soluble copolyamides. By replacing 30% by weight ofalkoxy alkyl modified polyamide 66 with alcohol soluble copolyamide likeSVP 637 or 651 (polymer A), Elvamide 8061, synergistic effects werefound. Fiber formation of the blend is more efficient than either of thecomponents alone. Soaking in ethanol and measuring filtration efficiencyshows better than 98% filtration efficiency retention, THC bench testingshowing comparable results with Type 8 polyamide alone. This type blendshows that we can obtain advantage of efficient fiber formation andexcellent filtration characteristic of copolyamide with advantage ofexcellent chemical resistance of crosslinked type 8 polyamide. Alcoholsoak test strongly suggests that non-crosslinkable copolyamide hasparticipated in crosslinking to maintain 98% of filtration efficiency.

DSC (see FIGS. 17-19 a) of blends of polymer A and B becomeindistinguishable from that of polymer A alone after they are heated to250° C. (fully crosslinked) with no distinct melt temperature. Thisstrongly suggests that blends of polymer A and B are a fully integratedpolymer by polymer B crosslinking with polymer A. This is a completelynew class of polyamide.

Similarly, melt-blend poly(ethylene terephthalate) with poly(butyleneterephthalate) can have similar properties. During the melt processingat temperatures higher than melt temperature of either component, estergroup exchange occurs and inter polymer of PET and PBT formed.Furthermore, our crosslinking temperature is lower than either of singlecomponent. One would not have expected that such group exchange occur atthis low temperature. Therefore, we believe that we found a new familyof polyamide through solution blending of Type A and Type B polyamideand crosslinking at temperature lower than the melting point of eithercomponent.

When we added 10% by weight of t-butyl phenol oligomer (Additive 7) andheat treated at temperature necessary for crosslinking temperature, wehave found even better results. We theorized that hydroxyl functionalgroup of t-butyl phenol oligomers would participate in reaction withfunctional group of type 8 nylons. What we have found is this componentsystem provides good fiber formation, improved resistance to hightemperature and high humidity and hydrophobicity to the surface of finefiber layers.

We have prepared samples of mixture of Polymer A and Polymer B (Sample6A) and another sample of mixture of Polymer A, Polymer B and Additive &(Sample 6B). We then formed fiber by electrospinning process, exposedthe fiber mat at 300° F. for 10 minutes and evaluated the surfacecomposition by ESCA surface analysis.

Table shows ESCA analysis of Samples 6A and 6B.

Composition (%) Sample 6A Sample 6B Polymer A 30 30 Polymer B 70 70Additive 7  0 10

Surface Composition W/O Heat W/Heat W/O Heat W/Heat Polymer A&B (%) 100100 68.9 43.0 Additive 7  0  0 31.1 57.0

ESCA provides information regarding surface composition, except theconcentration of hydrogen. It provides information on carbon, nitrogenand oxygen. Since the Additive 7 does not contain nitrogen, we canestimate the ratio of nitrogen containing polyamides and additive thatdoes not contain nitrogen by comparing concentration of nitrogen.Additional qualitative information is available by examining O 1sspectrum of binding energy between 535 and 527 eV. C═O bond has abinding energy at around 531 eV and C—O bond has a binding energy at 533eV. By comparing peak heights at these two peaks, one can estimaterelative concentration of polyamide with predominant C═O and additivewith solely C—O groups. Polymer B has C—O linkage due to modificationand upon crosslinking the concentration of C—O will decrease. ESCAconfirms such reaction had indeed occurred, showing relative decrease ofC—O linkage. (FIG. 4 for non heat treated mixture fiber of Polymer A andPolymer B, FIG. 5 for heat treated mixture fiber of Polymer A andPolymer B). When Additive 7 molecules are present on the surface, onecan expect more of C—O linkage. This is indeed the case as can be seenin FIGS. 6 and 7. (FIG. 6 for as-spun mixture fibers of Polymer A,Polymer B and Additive 7. FIG. 7 for heat treated mixture fibers ofPolymer A, Polymer B and Additive 7). FIG. 6 shows that theconcentration of C—O linkage increases for Example 7. The finding isconsistent with the surface concentration based on XPS multiplexspectrum of FIGS. 8 through 11.

It is apparent that t-butyl oligomer molecules migrated toward thesurface of the fine fibers and form hydrophobic coating of about 50 Å.Type 8 nylon has functional groups such as —CH₂OH and —CH₂OCH₃, which weexpected to react with —OH group of t-butyl phenol. Thus, we expected tosee less oligomer molecules on the surface of the fibers. We have foundthat our hypothesis was not correct and we found the surface of theinterpolymer has a thin coating.

Samples 6A, 6B and a repeat of sample described in Section 5 have beenexposed THC bench at 160° F. at 100% RH. In previous section, thesamples were exposed to 140° F. and 100% RH. Under these conditions,t-butyl phenol protected terpolymer copolyamide from degradation.However, if the temperature is raised to 160° F. and 100% RH, then thet-butyl phenol oligomer is not as good in protecting the underlyingterpolymer copolyamide fibers. We have compared samples at 160° F. and100% RH.

TABLE Retained Fine Fiber Efficiency after Exposure to 160° F. and 100%RH Sample After 1 Hr. After 2 Hrs. After 3 Hrs. Sample 6A 82.6 82.6 85.9Sample 6B 82.4 88.4 91.6 Sample 5 10.1The table shows that Sample 6B helps protect exposure to hightemperature and high humidity.

More striking difference shows when we exposed to droplets of water on afiber mat. When we place a drop of DI water in the surface of Sample 6A,the water drops immediately spread across the fiber mat and they wet thesubstrate paper as well. On the other hand, when we place a drop ofwater on the surface of Sample 6B, the water drop forms a bead and didnot spread on the surface of the mat. We have modified the surface ofSample 16 to be hydrophobic by addition of oligomers of p-t-butylphenol. This type of product can be used as a water mist eliminator, aswater drops will not go through the fine fiber surface layer of Sample6B.

Samples 6A, 6B and a repeat sample of Section 5 were placed in an ovenwhere the temperature was set at 310° F. Table shows that both Samples6A and 6B remain intact while Sample of Section 5 was severely damaged.

TABLE Retained Fine Fiber Efficiency after Exposure to 310° F. SampleAfter 6 Hrs. After 77 Hrs. Sample 6A 100% 100% Sample 6B 100% 100%Sample 5  34%  33%

While addition of oligomer to Polymer A alone improved the hightemperature resistance of fine fiber layer, the addition of Additive 7has a neutral effect on the high temperature exposure.

We have clearly shown that the mixture of terpolymer copolyamide, alkoxyalkyl modified nylon 66 and oligomers of t-butyl phenol provides asuperior products in helping fine fibers under severe environment withimproved productivity in manufacturing over either mixture of terpolymercopolyamide and t-butyl phenol oligomer or the mixture of terpolymercopolyamide and alkoxy alkyl modified nylon 66. These two componentsmixture are also improvement over single component system.

EXAMPLE 7 Compatible Blend of Polyamides and Bisphenol A polymers

A new family of polymers can be prepared by oxidative coupling ofphenolic ring (Pecora, A; Cyrus, W. U.S. Pat. No. 4,900,671(1990) andPecora, A; Cyrus, W.; Johnson, M. U.S. Pat. No. 5,153,298(1992)). Ofparticular interest is polymer made of Bisphenol A sold by Enzymol Corp.Soybean Peroxidase catalyzed oxidation of Bisphenol A can start fromeither side of two —OH groups in Bisphenol A. Unlike Bisphenol A basedpolycarbonate, which is linear, this type of Bisphenol A polymer formshyperbranched polymers. Because of hyperbranched nature of this polymer,they can lower viscosity of polymer blend.

We have found that this type of Bisphenol A polymer can be solutionblended with polyamides. Reported Hansen's solubility parameter fornylon is 18.6. (Page 317, Handbook of Solubility Parameters and othercohesion parameters, A. Barton ed., CRC Press, Boca Raton Fla., 1985) Ifone calculates solubility parameter (page 61, Handbook of SolubilityParameters), then the calculated solubility parameter is 28.0. Due tothe differences in solubility parameter, one would not expect that theywould be miscible with each other. However, we found that they are quitemiscible and provide unexpected properties.

50:50 blend of Bisphenol A resin of M.W. 3,000 and copolyamide was madein ethanol solution. Total concentration in solution was 10%.Copolyamide alone would have resulted in 0.2 micron fiber diameter.Blend resulted in lofty layer of fibers around 1 micron. Bisphenol A of7,000 M.W. is not stable with copolyamide and tends to precipitate.

DSC of 50:50 blend shows lack of melting temperature. Copolyamide hasmelting temperature around 150 degree C. and Bisphenol A resin is aglassy polymer with Tg of about 100. The blend shows lack of distinctmelting. When the fiber mat is exposed to 100 degree C., the fiber matdisappears. This blend would make an excellent filter media where upperuse temperature is not very high, but low-pressure drop is required.This polymer system could not be crosslinked with a reasonable manner.

EXAMPLE 8 Dual Roles of Bisphenol A Polymer As Solvent and Solid inBlend

A surprising feature of Bisphenol A polymer blend is that in solutionform Bisphenol A polymer acts like a solvent and in solid form thepolymer acts as a solid. We find dual role of Bisphenol A polymer trulyunique.

The following formulation is made:

Alkoxy alkyl modified PA 66: Polymer B  180 g Bisphenol A Resin (3,000MW): Polymer C  108 g Ethanol 190 Grade  827 g Acetone  218 g DI water 167 g Catalyst  9.3 g

The viscosity of this blend was 32.6 centipoise by Brookfieldviscometer. Total polymer concentration was be 19.2%. Viscosity ofPolymer B at 19.2% is over 200 centipoise. Viscosity of 12% polymer Balone in similar solvent is around 60 centipoise. This is a clearexample that Bisphenol A resin acts like a solvent because the viscosityof the total solution was lower than expected. Resultant fiber diameterwas 0.157 micron. If polymer B alone participated in fiber formation,the expected fiber size would be less than 0.1 micron. In other words,Polymer C participated in fiber formation. We do not know of any othercase of such dramatic dual role of a component. After soaking the samplein ethanol, the filtration efficiency and fiber size was measured. Afteralcohol soak, 85.6% of filtration efficiency was retained and the fibersize was unchanged. This indicates that Polymer C has participated incrosslinking acting like a polymer solid.

Another polymer solution was prepared in the following manner:

Alkoxy alkyl Modified PA66: Polymer B  225 g Bisphenol A Resin (3,000MW): Polymer C  135 g Ethanol 190 Grade  778 g Acetone  205 g DI Water 157 g Catalyst 11.6 g

Viscosity of this blend was 90.2 centipoise. This is a very lowviscosity value for 24% solid. Again, this is an indication Polymer Cacts like a solvent in the solution. However, when they are electrospuninto fiber, the fiber diameter is 0.438 micron. 15% solution of PolymerB alone would have produced around 0.2-micron fibers. In final state,Polymer C contributes to enlarging fiber sizes. Again, this exampleillustrates that this type of branched polymer acts as a solvent insolution and acts as a solid in final state. After soaking in ethanolsolution, 77.9% of filtration efficiency was retained and fiber size wasunchanged.

EXAMPLE 9 Development of Crosslinked Polyamides/Bisphenol A PolymerBlends

Three different samples were prepared by combining resins, alcohols andwater, stirring 2 hours at 60 degree C. The solution is cooled to roomtemperature and catalyst was added to solution and the mixture wasstirred another 15 minutes. Afterward, viscosity of solution wasmeasured and spun into fibers.

The following table shows these examples:

Recipe (g) Sample 9A Sample 9B Sample 9C Polymer B 8.4 12.6 14.7 PolymerA 3.6 5.4 6.3 Polymer C 7.2 10.8 12.6 Ethanol 190 Grade 89.3 82.7 79.5Isopropanol 23.5 21.8 21.0 DI Water 18.0 16.7 15.9 Catalyst .45 0.580.79 Viscosity (cP) 22.5 73.5 134.2 Fiber Size (micron) 0.14 0.258 0.496

We have found out that this blend generates fibers efficiently,producing about 50% more mass of fiber compared to Polymer A recipe. Inaddition, resultant polymeric microfibers produce a more chemicallyresistant fiber. After alcohol soak, a filter made from these fibersmaintained more than 90% filtration efficiency and unchanged fiberdiameter even though inherently crosslinkable polymer is only 44% of thesolid composition. This three-polymer composition of co-polyamide,alkoxy alkyl modified Nylon 66 and Bisphenol A creates excellent fiberforming, chemically resistant material.

EXAMPLE 10 Alkoxy alkyl Modified Co-polymer of Nylon 66 and Nylon 46

In a 10-gallon high-pressure reactor, the following reactions were made,and resultant polymers were analyzed. After reaction temperature wasreached, catalyst were added and reacted for 15 minutes. Afterward, thepolymer solution was quenched, precipitated, washed and dried.

Reactor Charge (LB) Run 10A Run 10B Run 10C Run 10D Run 10E Nylon 4,6(duPont Zytel 101) 10 5 5 5 5 Nylon 6,6 (DSM Stanyl 300) 0 5 5 5 5Formaldehyde 8 10 8 10 8 DI Water 0.2 0.2 2 0.2 2 Methanol 22 20 20 2020 Reaction Temp (C.°) 140 140 140 150 150 Tg (C.°) 56.7 38.8 37.7 38.531.8 Tm (C.°) 241.1 162.3 184.9 175.4 189.5 Level of Substitution Alkoxy(wt. %) 11.9 11.7 7.1 11.1 8.4 Methylol (wt %) 0.14 0.13 0.14 0.26 0.24

DSC of the polymer made with Nylon 46 and Nylon 66 shows broad singlemelt temperature, which are lower than the melting temperature ofmodified Nylon 46 (241° C.) or modified Nylon 66 (210° C.). This is anindication that during the reaction, both components are randomlydistributed along the polymer chain. Thus, we believe that we haveachieved random copolymer of Nylon 46 and Nylon 66 with alkoxy alkylmodification. These polymers are soluble in alcohols and mixtures ofalcohol and water.

Property ASTM Nylon 6.6 Nylon 4.6 T_(m) 265° C. 295° C. Tensile StrengthD638 13.700 8.500 Elongation at Break D638 15-80 60 Tensile YieldStrength D638   8000-12,000 Flexural Strength D790 17,8000 11,500Tensile Modulus × 10³ psi D638 230-550 250 Izod Impact ft-lb/in of notchD256A 0.55-1.0  17 Deflection Temp Under D648 158 194 Flexural Load 264psiBoth are highly crystalline and are not soluble in common alcohols.Source: Modern Plastics Encyclopedia 1998

EXAMPLE 11 Development of Interpolymer of Copolyamides and AlkoxyalkylModified Nylon 46/66 Copolymer and Formation of Electrospun Fibers

Runs 10B and 10D samples were made into fibers by methods described inabove. Alkoxy alkyl modified Nylon 46/66 (Polymer D) alone weresuccessfully electrospun. Blending Polymer D with Polymer A bringsadditional benefits of more efficient fiber formation and ability tomake bigger fibers without sacrificing the crosslinkability of Polymer Das can be seen in the following table:

Polymer 10B Polymer 10D w/30% w/30% Alone Polymer A Alone Polymer AFiber Size (micron) 0.183 0.464 0.19 0.3 Fiber Mass Ratio 1 3 1 2Filtration Effi. Retention (%) 87 90 92 90 Fiber Mass Ratio iscalculated by (total length of fiber times cross sectional area).Filtration Efficiency Retention is measured soaking filter sample inethanol. Fiber size was unchanged by alcohol soak.

EXAMPLE 12 Crosslinked, Electrospun PVA

PVA powders were purchased from Aldrich Chemicals. They were dissolvedeither in water or 50/50 mixture of methanol and water. They were mixedwith crosslinking agent and toluene sulfonic acid catalyst beforeelectrospinning. The resulting fiber mat was crosslinked in an oven at150° C. for 10 minutes before exposing to THC bench.

Sample 12A Sample 12B Sample 12C Sample 12D PVA Hydrolysis 98-99 87-8987-89 87-89 M.W. 31,500-50,000 31,500-50,000 31,500-50,000 31,500-50,000PVA. (wt. -%) 10 10 10 10 Solvent Water Mixture Mixture (c) Mixture (d)Other Polymer None None Acrylic Acid Cymel 385 Other Polymer/  0  0 3030 PVA (%) Fiber Retained 0 (a) 0 (a, b) 95 (b) 20 (b) THC, 1 hr. (%)Fiber Retained THC, 90 (a) 3 hr. (%) (a): Temperature 160° F., 100%humidity (b): Temperature 140° F., 100% humidity (c): Molecular Weight2000 (d): Melamine formaldehyde resin from Cytec

EXAMPLE 13

A conventional cellulose air filter media was used as the substrate.This substrate had a basis weight of 67 pounds per 3000 square feet, aFrazier permeability of 16 feet per minute at 0.5 inches of waterpressure drop, a thickness of 0.012 inches, and a LEFS efficiency of41.6%. A fine fiber layer of Example 1 was added to the surface usingthe process described with a nominal fiber diameter of 0.2 microns. Theresulting composite had a LEFS efficiency of 63.7%. After exposure to140F air at 100% relative humidity for 1 hour the substrate only samplewas allowed to cool and dry, it then had a LEFS efficiency of 36.5%.After exposure to 140 F air at 100% relative humidity for 1 hour thecomposite sample was allowed to cool and dry, it then had a LEFSefficiency of 39.7%. Using the mathematical formulas described, the finefiber layer efficiency retained after 1 hour of exposure was 13%, thenumber of effective fine fibers retained was 11%.

EXAMPLE 14

A conventional cellulose air filter media was used as the substrate.This substrate had a basis weight of 67 pounds per 3000 square feet, aFrazier permeability of 16 feet per minute at 0.5 inches of waterpressure drop, a thickness of 0.012 inches, and a LEFS efficiency of41.6%. A fine fiber layer of Example 5 was added to the surface usingthe process described with a nominal fiber diameter of 0.2 microns. Theresulting composite had a LEFS efficiency of 96.0%. After exposure to160 F air at 100% relative humidity for 3 hours the substrate onlysample was allowed to cool and dry, it then had a LEFS efficiency of35.3%. After exposure to 160 F air at 100% relative humidity for 3 hoursthe composite sample was allowed to cool and dry, it then had a LEFSefficiency of 68.0%. Using the mathematical formulas described, the finefiber layer efficiency retained after 3 hours of exposure was 58%, thenumber of effective fine fibers retained was 29%.

EXAMPLE 15

A conventional cellulose air filter media was used as the substrate.This substrate had a basis weight of 67 pounds per 3000 square feet, aFrazier permeability of 16 feet per minute at 0.5 inches of waterpressure drop, a thickness of 0.012 inches, and a LEFS efficiency of41.6%. A fine fiber layer of a blend of Polymer A and Polymer B asdescribed in Example 6 was added to the surface using the processdescribed with a nominal fiber diameter of 0.2 microns. The resultingcomposite had a LEFS efficiency of 92.9%. After exposure to 160 F air at100% relative humidity for 3 hours the substrate only sample was allowedto cool and dry, it then had a LEFS efficiency of 35.3%. After exposureto 160 F air at 100% relative humidity for 3 hours the composite samplewas allowed to cool and dry, it then had a LEFS efficiency of 86.0%.Using the mathematical formulas described, the fine fiber layerefficiency retained after 3 hours of exposure was 96%, the number ofeffective fine fibers retained was 89%.

EXAMPLE 16

A conventional cellulose air filter media was used as the substrate.This substrate had a basis weight of 67 pounds per 3000 square feet, aFrazier permeability of 16 feet per minute at 0.5 inches of waterpressure drop, a thickness of 0.012 inches, and a LEFS efficiency of41.6%. A fine fiber layer of Polymer A, Polymer B, t-butyl phenololigomer as described in Example 6 was added to the surface using theprocess described with a nominal fiber diameter of 0.2 microns. Theresulting composite had a LEFS efficiency of 90.4%. After exposure to160 F air at 100% relative humidity for 3 hours the substrate onlysample was allowed to cool and dry, it then had a LEFS efficiency of35.3%. After exposure to 160 F air at 100% relative humidity for 3 hoursthe composite sample was allowed to cool and dry, it then had a LEFSefficiency of 87.3%. Using the mathematical formulas described, the finefiber layer efficiency retained after 3 hours of exposure was 97%, thenumber of effective fine fibers retained was 92%.

EXAMPLE 17

A conventional cellulose air filter media was used as the substrate.This substrate had a basis weight of 67 pounds per 3000 square feet, aFrazier permeability of 16 feet per minute at 0.5 inches of waterpressure drop, a thickness of 0.012 inches, and a LEFS efficiency of41.6%. A fine fiber layer of crosslinked PVA with polyacrylic acid ofExample 12 was added to the surface using the process described with anominal fiber diameter of 0.2 microns. The resulting composite had aLEFS efficiency of 92.9%. After exposure to 160 F air at 100% relativehumidity for 2 hours the substrate only sample was allowed to cool anddry, it then had a LEFS efficiency of 35.3%. After exposure to 160 F airat 100% relative humidity for 2 hours the composite sample was allowedto cool and dry, it then had a LEFS efficiency of 83.1%. Using themathematical formulas described, the fine fiber layer efficiencyretained after 2 hours of exposure was 89%, the number of effective finefibers retained was 76%.

EXAMPLE 18

The following filter medias have been made with the methods described inExample 1-17.

Filter Media Examples Substrate perm Substrate Basis wt SubstrateSubstrate Composite Substrate (Frazier) (lbs/3000 sq ft) Thickness (in)Eff (LEFS) Eff (LEFS) Single fine fiber layer on (+/−10%) (+/−10%)(+/−25%) (+/−5%) (+/−5%) single substrate (flow either direction throughmedia Cellulose air filter media 58 67 0.012 11% 50% Cellulose airfilter media 16 67 0.012 43% 58% Cellulose air filter media 58 67 0.01211% 65% Cellulose air filter media 16 67 0.012 43% 70% Cellulose airfilter media 22 52 0.010 17% 70% Cellulose air filter media 16 67 0.01243% 72% Cellulose/synthetic blend 14 70 0.012 30% 70% with moistureresistant resin Flame retardant cellulose 17 77 0.012 31% 58% air filtermedia Flame retardant cellulose 17 77 0.012 31% 72% air filter mediaFlame retardant synthetic 27 83 0.012 77% air filter media SpunbondRemay 1200 15 0.007  5% 55% (polyester) Synthetic/cellulose air 260 760.015  6% 17% filter media Synthetic/glass air filter 31 70 0.012 55%77% media Synthetic/glass air filter 31 70 0.012 50% 90% media Synthetic(Lutrador- 300 25 0.008  3% 65% polyester) Synthetic (Lutrador- 0.01690% polyester)

Media has been used flat, corrugated, pleated, corrugated and pleated,in flatsheets, pleated flat panels, pleated round filters, and otherfilter structures and configurations.

Test Methods

Hot Water Soak Test

Using filtration efficiency as the measure of the number of fine fiberseffectively and functionally retained in structure has a number ofadvantages over other possible methods such as SEM evaluation.

the filtration measure evaluates several square inches of media yieldinga better average than the tiny area seen in SEM photomicrographs(usually less than 0.0001 square inch

the filtration measurement quantifies the number of fibers remainingfunctional in the structure. Those fibers that remain, but are clumpedtogether or otherwise existing in an altered structure are only includedby their measured effectiveness and functionality.

Nevertheless, in fibrous structures where the filtration efficiency isnot easily measured, other methods can be used to measure the percent offiber remaining and evaluated against the 50% retention criteria.

Description:

This test is an accelerated indicator of filter media moistureresistance. The test uses the LEFS test bench to measure filter mediaperformance changes upon immersion in water. Water temperature is acritical parameter and is chosen based on the survivability history ofthe media under investigation, the desire to minimize the test time andthe ability of the test to discriminate between media types. Typicalwater temperatures re 70° F., 140° F. or 160° F.

Procedure:

A 4″ diameter sample is cut from the media. Particle capture efficiencyof the test specimen is calculated using 0.8 μm latex spheres as a testchallenge contaminant in the LEFS (for a description of the LEFS test,see ASTM Standard F1215-89) bench operating at 20 FPM. The sample isthen submerged in (typically 140° F.) distilled water for 5 minutes. Thesample is then placed on a drying rack and dried at room temperature(typically overnight). Once it is dry the sample is then retested forefficiency on the LEFS bench using the same conditions for the initialcalculation.

The previous steps are repeated for the fine fiber supporting substratewithout fine fiber.

From the above information one can calculate the efficiency componentdue only to the fine fiber and the resulting loss in efficiency due towater damage. Once the loss in efficiency due to the fine fiber isdetermined one can calculate the amount of efficiency retained.

Calculations:

-   Fine fiber layer efficiency: E_(i)=Initial Composite Efficiency;    -   E_(s)=Initial Substrate Efficiency;    -   F_(e)=Fine Fiber Layer    -   F_(e)=1−EXP(Ln(1−E_(i))−Ln(1−E_(x)))-   Fine fiber layer efficiency retained: F_(i)=Initial fine fiber layer    efficiency;    -   F_(x)=Post soak fine fiber layer efficiency;    -   F_(r)=Fine fiber retained        F _(r) =F _(x) /F _(i)        The percentage of the fine fibers retained with effective        functionality can also be calculated by:        %=log(1−F _(x))/log(1−F _(i))        Pass/Fail Criteria: >50% efficiency retention

In most industrial pulse cleaning filter applications the filter wouldperform adequately if at least 50% of the fine fiber efficiency isretained.

THC Bench (Temperature, Humidity

Description: The purpose of this bench is to evaluate fine fiber mediaresistance to the affects of elevated temperature and high humidityunder dynamic flow conditions. The test is intended to simulate extremeoperating conditions of either an industrial filtration application, gasturbine inlet application, or heavy duty engine air intake environments.Samples are taken out, dried and LEFS tested at intervals. This systemis mostly used to simulate hot humid conditions but can also be used tosimulate hot/cold dry situations.

Temperature −31 to 390° F. Humidity    0 to 100% RH (Max temp for 100%RH is 160° F. and max continuous duration at this condition is 16 hours)Flow Rate    1 to 35 FPMProcedure:

A 4″ diameter sample is cut from the media.

Particle capture efficiency of the test specimen is calculated using 0.8μm latex spheres as a test challenge contaminant in the LEFS benchoperating at 20 FPM.

The sample is then inserted into the THC media chuck.

Test times can be from minutes to days depending on testing conditions.

The sample is then placed on a drying rack and dried at room temperature(typically overnight). Once it is dry the sample is then retested forefficiency on the LEFS bench using the same conditions for the initialcalculation.

The previous steps are repeated for the fine fiber supporting substratewithout fine fiber.

From the above information one can calculate the efficiency componentdue only to the fine fiber and the resulting loss in efficiency due toalcohol damage.

Once the loss in efficiency due to the fine fiber is determined one cancalculate the amount of efficiency retained.

Pass/Fail Criteria: >50% efficiency retention

In most industrial pulse cleaning filter applications the filter wouldperform adequately if at least 50% of the fine fiber efficiency isretained.

Alcohol (Ethanol) Soak Test

Description: The test uses the LEFS test bench to measure filter mediaperformance changes upon immersion in room temperature ethanol.

Procedure:

A 4″ diameter sample is cut from the media. Particle capture efficiencyof the test specimen is calculated using 0.8 μm latex spheres as a testchallenge contaminant in the LEFS bench operating at 20 FPM. The sampleis then submerged in alcohol for 1 minute.

The sample is then placed on a drying rack and dried at room temperature(typically overnight). Once it is dry the sample is then retested forefficiency on the LEFS bench using the same conditions for the initialcalculation. The previous steps are repeated for the fine fibersupporting substrate without fine fiber. From the above information onecan calculate the efficiency component due only to the fine fiber andthe resulting loss in efficiency due to alcohol damage. Once the loss inefficiency due to the fine fiber is determined one can calculate theamount of efficiency retained.

Pass/Fail Criteria: >50% efficiency retention.

The above specification, examples and data provide an explanation of theinvention. However, many variations and embodiments can be made to thedisclosed invention. The invention is embodied in the claims hereinafter appended.

1. A filter element comprising: (a) a media pack comprising: (i) aconstruction of a media composite; said construction including asubstrate having a plurality of pleats having a length extending fromsaid first end to said second end, the substrate comprising a filtermedium having an efficiency when tested with particles having a diameterof 0.01 to 1 μm; (ii) said construction having a tubular shape anddefining an open interior having a first and a second opposite ends; and(iii) said substrate at least partially covered by a single layer, saidlayer comprising a polymeric fine fiber comprising a fiber with adiameter of about 0.01 to 0.5 microns such that after test exposure fora test period of 16 hours to test conditions of 140° F. air and arelative humidity of 100% retains greater than 30% of the fiberunchanged for filtration purposes, the fine fiber comprising acrosslinked polyvinylalcohol; (b) a first end cap and a second end cap;(i) said media pack being secured to said first end cap at said firstend of said media pack; (ii) said media pack being secured to saidsecond end cap at said second end of said media pack; (iii) at least oneof said first and second end caps including a sealing portion; saidsealing portion comprising a material compressible in a direction towardsaid media pack.
 2. The element of claim 1 wherein the polymeric fibercomprises a polyvinylalcohol having a degree of hydrolysis of about87-99.9%.
 3. The element of claim 2 wherein the polyvinylalcohol iscrosslinked with about 1 to 40 wt. % of a crosslinking agent.
 4. Theelement of claim 1 wherein the polymeric fiber comprises a superhydrolyzed polyvinylalcohol.
 5. The element of claim 2 wherein thecrosslinked polyvinylalcohol is crosslinked using a polyacrylic acidhaving a molecular weight of about 1000 to
 3000. 6. The element of claim2 wherein the crosslinked polyvinylalcohol is crosslinked using amelamine-formaldehyde resin having a molecular weight of about 1000 to3000.
 7. The element of claim 1 wherein the polymeric fiber alsocomprises a resinous additive comprising an oligomer having a molecularweight of about 500 to 3000 and an aromatic character wherein theadditive is miscible with the polymer but forms a hydrophobic coating onthe fiber.
 8. The element of claim 7 wherein the resinous additivecomprises an alkyl phenolic aromatic character wherein the additiveforms a hydrophobic coating on the fiber.
 9. The element of claim 7wherein the additive comprises an oligomer comprising tertiary butylphenol.
 10. The element of claim 7 wherein the resin comprises anoligomer comprising bis-phenol A.
 11. The element of claim 7 wherein theresin comprises an oligomer comprising dihydroxy biphenyl.
 12. Theelement of claim 7 wherein the additive comprises a blend of theresinous additive and a fluoropolymer.
 13. The element of claim 7wherein the additive comprises a fluorocarbon surfactant.
 14. Theelement of claim 7 wherein the additive comprises a nonionic surfactant.15. The element of claim 7 wherein the polymeric fine fiber comprises apolyurethane polymer.